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Plain English

The AI glossary

Every term the guide leans on, defined the way we would explain it across a desk. No prior AI background assumed.

353 terms, plain English

01Reader paths
  • New to AI

    The words that turn up in the first week, in the order they usually turn up.

    • AI (artificial intelligence)

      Software that does work we used to assume needed a person, such as writing, summarising, reading images or judging what a request means.

    • Generative AI

      AI that produces new text, images, audio or code rather than only sorting or scoring things that already exist.

    • Large language model (LLM)

      A model trained on very large amounts of text to predict what comes next, which is what lets it write, summarise, translate and answer questions.

    5 more
    • Prompt

      What you type to an AI assistant: the request plus any context you include.

    • Token

      The unit models actually read and write: a short chunk of text, roughly three-quarters of an English word on average.

    • Context window

      The amount of text a model can consider at once: your conversation, any documents you attach, and its own replies.

    • Hallucination

      When a model states something false as if it were certain: an invented citation, a wrong date, a plausible-sounding statistic.

    • AI assistant

      An AI product with its own chat surface that you go to and ask, handling many kinds of task rather than one.

  • Choosing an AI tool

    What a vendor means on the pricing page, and what to ask before you commit.

    • AI use case

      One specific job you intend AI to do, defined narrowly enough that you could tell whether it worked.

    • Proof of concept (PoC)

      A small build to test whether an idea works at all, deliberately short of production quality and often mistaken for it.

    • Evals

      Structured tests that measure whether an AI system actually does its job, and the honest answer to how you would know if it stopped.

    5 more
    • Seat based pricing

      Paying a fixed amount per person per month, predictable to budget for and wasteful when only some of those people use it.

    • Usage based pricing

      Paying for what you actually consume, which rewards light use and can surprise you in a busy month without a cap in place.

    • Total cost of ownership (TCO)

      Everything a tool costs over its life, including setup, training, integration and the staff time to run it, not only the licence.

    • Vendor lock in

      How hard it would be to move off a tool later, worth weighing while switching is still cheap rather than when it is not.

    • Buy versus build

      The choice between paying for a finished tool and assembling your own, usually decided by whether the capability is core to you.

  • Running AI safely

    The questions your legal and security colleagues will ask, defined before they do.

    • Shadow AI

      Staff using AI tools the organisation has not approved, usually with good intentions, and the reason many first policies get written.

    • AI policy

      The written document telling staff what they may and may not do with AI tools, usually the cheapest first control to put in place.

    • Data privacy in AI

      What happens to the text, files and recordings you put into an AI tool: who can see them, how long they are kept, and whether they train the model.

    5 more
    • Data residency

      A commitment about which country your data is stored in, usually the first question asked in regulated work and in the public sector.

    • Retention policy

      How long a vendor keeps your inputs and outputs before deleting them, and whether you can change that period.

    • Prompt injection

      Hidden instructions planted in content a model reads, aiming to make it ignore its real task, and the central security problem of AI tools.

    • Human-in-the-loop (HITL)

      Designing an automated process so a person approves or corrects specific steps rather than only seeing the result.

    • Audit trail

      A durable record of who did what and when, which is what turns a claim about how a system was used into evidence.

A to Z

Pick a letter to see those terms, or All to read the whole list.

02Next

Terms are step one. When you want the tools rather than the vocabulary, the guide answers that side.

How these definitions are written and checked: how we review.