AI architecture glossary
Every term the course teaches, defined in plain English, in one place. Each entry links to the module that explains it properly; the definitions here are the short version, written to stand alone.
- Adapter
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A small file of extra numbers trained alongside a model, changing its habits without altering the original weights. Cheaper to produce than retraining the model, portable, and small enough to keep several of them, one per task. Usually produced by a method called LoRA.
- Agent
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An AI system given a goal, a set of tools, and permission to work in a loop: plan a step, act, observe the result, and repeat until done, blocked, or handed to a person.
- Alignment
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The training that shapes a model’s behaviour towards being helpful and refusing harm. Genuinely strong, genuinely incomplete, which is why production systems add checks outside the model.
- Approximate nearest neighbour
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The compromise that keeps vector search fast at scale. Rather than comparing a question against every stored passage, the store checks a small set of likely candidates and returns what is probably nearest. Usually that is the same answer; occasionally it is not, and the balance between speed and thoroughness is a setting somebody can change.
- Backfill
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Re-running a pipeline over a stretch of past data after a fix, so the correction reaches the history and not only today. Whether one is possible decides how expensive a changed definition turns out to be.
- Chunking
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Splitting documents into short passages, ideally one idea each, so retrieval can find precisely rather than approximately.
- Context window
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The model's working memory: the maximum number of tokens it can consider at once, covering instructions, the conversation, supplied documents, and the answer as it grows.
- Cosine similarity
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The usual measure of how alike two embeddings are, scored between zero and one by asking how strongly they point in the same direction.
- Data lake
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Storage that accepts everything in its raw form and applies structure later. Flexible and cheap; a swamp without curation.
- Data pipeline
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Automated plumbing that copies data between systems and reshapes it on the way, applying definitions as it goes. It fails quietly, which is why monitoring and ownership matter.
- Data residency
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Where your data is stored and processed geographically, and whose law applies to it there. A contract question before it is a technology question.
- Data warehouse
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Storage that demands clean, agreed structure before data enters, which makes reporting fast and consistent, and the warehouse rigid.
- Deterministic
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Describes a process that produces the same result from the same input, every time. Rules, calculations, and ordinary code are deterministic; a language model is not, which is why exact work is given to exact tools and judgement is given to the model.
- Embedding
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A long list of numbers capturing what a passage is about, produced by a model trained so that texts with similar meaning land near each other numerically.
- EU AI Act
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European law whose obligations scale with the risk of the use case: a few uses prohibited, high-risk uses carrying oversight and documentation duties, transparency for most of the rest.
- Evaluation
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Measuring an AI system against a set of real questions with agreed good answers, on a schedule and after every change, so decline is detected rather than reported.
- Fine-tuning
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Additional training on your own examples that adjusts the model's weights, changing its habits rather than its knowledge.
- Frontier model
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The most capable tier of models available at a given moment. The frontier moves; the label follows capability, not any one product.
- Golden question set
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A fixed set of real questions with agreed good answers, run against a system on a schedule and after every change. The working tool of evaluation, including questions the system must answer and questions it must refuse.
- Groundedness
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Whether the claims in an answer are supported by the passages the system retrieved. Production systems check it mechanically before delivering.
- Guardrails
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The controls wrapped around an AI system: permissions, approval gates, budgets, audit logs, and the input and output checks around every model call.
- Hallucination
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A fluent, confident, wrong answer produced when a model completes a pattern beyond its knowledge.
- Human-in-the-loop
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Autonomy assigned per class of action, with a person approving anything consequential until months of evidence justify loosening, class by class.
- Hybrid search
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Retrieval that pairs meaning-based similarity with keyword matching, because product codes, names, and exact phrases defeat embeddings alone.
- Idempotency
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The property that makes a pipeline step safe to run again: once or five times, the result is the same. Without it, an automatic retry after a failure quietly duplicates data.
- Inference
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Running a trained model to produce output. Training happens once; inference happens on every use, which is why it is where the running costs live.
- ISO 42001
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A management system standard certifying that an organisation runs AI deliberately: risks assessed and owned, decisions documented, performance reviewed.
- Jailbreak
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A crafted request designed to talk a model past its trained-in refusals. The reason output checking never relies on the model’s own judgement alone.
- Judge model
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A second model that reads an exchange and scores it against policy. The most capable check available, and the most expensive, so it is spent selectively.
- Lakehouse
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Lake storage underneath, with warehouse-style structure and guarantees applied only to the data that needs them. The default pattern for new analytical builds.
- Large language model
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A system trained on a vast amount of text to predict the next token. Its compressed patterns reproduce grammar, style, and knowledge, along with confident errors where the patterns run out.
- Lineage
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The ability to trace where a number came from and what transformed it on the way, so an auditor’s question has an answer.
- Machine learning
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Software that learns patterns from data rather than following hand-written rules. Predictive machine learning scores and forecasts; generative AI is the branch that produces text and media.
- Model Context Protocol
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An open standard giving systems a common way to describe their tools to any model, replacing per-vendor integration the way one plug standard replaces a drawer of cables.
- Model drift
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The quiet decay of a predictive model as the world moves away from the history it learned. Found by monitoring, never by waiting for complaints.
- Open-weights model
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A model whose weights are published for anyone to download and run, either on infrastructure you administer or on compute you rent for the purpose, trading supplier convenience for control.
- Predictive AI
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Models that learn from historical data to score or forecast: arrears risk, fraud, demand, churn. Evaluated by outcomes across affected groups and monitored for drift, not judged by fluency.
- Prompt
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Everything placed in front of a model for one request: the standing instructions, the question, and any supporting material.
- Prompt caching
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A supplier feature that processes the unchanging start of a prompt once and stores the result, so repeat requests skip re-reading it. It makes long standing instructions nearly free after the first call.
- Prompt engineering
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The craft of writing and testing the instructions, examples, and supporting material placed in front of a model, including the defensive share.
- Prompt injection
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Instructions hidden inside content a system reads, planted to hijack its behaviour. The indirect form arrives through retrieved documents, which is why retrieval systems treat content as data, never instructions.
- Retrieval-Augmented Generation (RAG)
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The pattern of retrieving relevant passages from your own documents and passing them to the model with instructions to answer from that material and cite it.
- Reasoning model
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A model that spends extra computation working through a problem before answering, trading speed and cost for performance on hard tasks. Priced accordingly.
- Re-ranking
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A careful second pass over a retrieval shortlist, promoting passages that answer the question over passages that merely resemble it.
- Reserved compute
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Machines rented for your exclusive use, in a region you name, running a model you chose. The middle arrangement between a shared API and hardware of your own: you pick the model and pay for the capacity whether or not you use it, and someone else keeps the machines running.
- Streaming
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Delivering a reply token by token as it is generated rather than waiting for the whole answer. In tension with output checking, which wants the complete draft first.
- System prompt
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The standing instructions placed before every conversation. In production systems a large share of it is defensive: what to refuse, how to treat retrieved content, when to hand over to a person.
- Temperature
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The setting controlling how much randomness enters a model’s choice of next token. Low is predictable and repetitive; high is varied and surprising.
- Token
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A short fragment of text, the unit models read, bill by, and measure context windows in. English averages roughly three quarters of a word per token.
- Tool use
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The convention that turns model text into action: the model emits a structured request naming a tool and its inputs, and the surrounding system, not the model, executes it.
- Unstructured data
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Information without a fixed shape: documents, emails, transcripts, images. What warehouses were built to exclude and AI systems consume.
- Vector store
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A database built to answer one question quickly: which stored items are nearest to this one? The home of embeddings in a retrieval system.
- Vendor lock-in
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The accumulated cost of leaving a supplier. Managed by keeping the portable things portable: your corpus, your prompts, your golden question set.
- Weights
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The billions of internal numbers adjusted during training that hold everything a model learned. Frozen when training ends, until someone retrains.