The Vocabulary

Every word you keep nodding along to.

Tokens, context windows, agents, RAG, hallucinations — what they actually mean in plain English, and why each one matters to you.

Plain English glossary

32+ terms, from basics to builder jargon.

Grouped by topic so you can skim what you need — or search when you hear something in a meeting and don't want to ask. No textbook tone, just what each word means and why it matters.

34
terms defined
5
topic groups
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searchable

The basics

The words everyone uses before anything else makes sense.

Artificial Intelligence (AI)

Basics

Software that does things we used to think required a human — understanding language, recognizing images, making decisions. Today it usually means systems that learn patterns from huge amounts of data rather than following hand-written rules.

Large Language Model (LLM)

Basics

The engine behind ChatGPT, Claude, and Gemini. It’s a system trained on enormous amounts of text that predicts what words should come next — which, at scale, lets it answer questions, write, and reason.

Example

When you chat with ChatGPT, you’re talking to an LLM.

Model

Basics

A single trained “brain” with a name and version — like Claude Opus or GPT-5. Newer or bigger models are generally more capable (and usually cost more to run).

Prompt

Basics

Whatever you type or say to the AI — your question, instruction, or request. The quality of your prompt largely decides the quality of the answer.

Token

Basics

The small chunks of text an AI reads and writes in — roughly three-quarters of a word each. AI usage and pricing are measured in tokens, not words.

Example

“Piazza Consulting” is about 4 tokens.

Context window

Basics

How much text the model can hold in mind at once — your message, the documents you paste, and the conversation so far. Go past it and the earliest parts start dropping off.

Example

Why a very long chat can “forget” what you said at the start.

Training data

Basics

The mountain of text and images a model learned from. It shapes what the model knows — and it has a cutoff date, which is why a model may not know recent events unless it can search.

Parameters

Basics

The internal dials a model adjusts as it learns — often billions of them. More parameters can mean more capability, but it’s not the only thing that matters.

How it works & behaves

What actually happens when you hit enter — and how models behave.

Inference

How it works

The act of actually running the model to get an answer. “Training” is teaching the model once; “inference” is using it, every time you hit enter.

System prompt

How it works

Hidden background instructions that set the AI’s role and rules before you ever type — its “job description” for the conversation.

Example

A support bot has a system prompt telling it to stay polite and only discuss that company’s products.

Temperature

How it works

A setting for how predictable vs. creative the output is. Low temperature = safe and consistent; high = more varied and surprising.

Multimodal

How it works

A model that handles more than text — images, audio, sometimes video. It’s why you can show an AI a photo and ask what’s in it.

Fine-tuning

How it works

Taking a general model and training it a little more on your specific data or style, so it specializes — like sending a smart generalist to a short, focused course.

Reasoning model

How it works

A newer kind of model that “thinks” before answering — working through steps internally. Slower, but much better at hard logic, math, and multi-step problems.

Chain-of-thought

How it works

Getting a model to show or work through its reasoning step by step instead of blurting a final answer. It reliably improves accuracy on tricky questions.

Example

Adding “think it through step by step” to a prompt.

Benchmark

How it works

A standardized test used to compare models on things like coding or reasoning. Useful, but real-world performance can differ from the leaderboard.

The new stuff

Agents, RAG, MCP — the terms dominating current conversations.

Agent / Agentic AI

New

AI that doesn’t just chat — it takes actions. It can use tools, browse, run code, and complete multi-step tasks on its own, checking its work as it goes. The big shift of 2025–2026.

Example

“Book the cheapest flight and add it to my calendar” — and it actually does it.

RAG (Retrieval-Augmented Generation)

New

A setup that lets a model pull answers from your documents instead of only its training. It looks up the relevant material first, then answers from it — which cuts down on made-up answers.

Example

A company chatbot that answers from your internal handbook.

Embeddings

New

A way of turning text into numbers that capture meaning, so a computer can tell that “car” and “automobile” are close. The quiet machinery behind smart search and RAG.

Vector database

New

A specialized store for those meaning-numbers, so an AI can instantly find the most relevant passages across thousands of documents.

MCP (Model Context Protocol)

New

A common standard that lets AI assistants plug into other tools and data sources — your calendar, your files, a database — like a universal adapter for connecting AI to the things you use.

On-prem / local model

New

Running AI on your own computers instead of a vendor’s cloud, so sensitive data never leaves your network. The serious answer for regulated industries.

Example

A hospital running AI in-house so patient data stays put.

Open vs. closed model

New

“Open” models can be downloaded and run yourself; “closed” ones are used through a company’s service. Open gives control and privacy; closed often gives top performance with less hassle.

GPU

New

The specialized chip that makes AI fast. Originally built for video games, now the workhorse of training and running large models — and the reason AI infrastructure is expensive.

When it goes wrong

Know these before you trust output blindly or paste sensitive data.

Hallucination

Watch out

When an AI states something false as if it were fact — a fake citation, a wrong number, an invented quote — delivered with total confidence. The single most important thing to watch for.

Example

Why you verify any name, figure, or legal citation it gives you.

Prompt injection

Watch out

A security attack where hidden instructions buried in a webpage, email, or document trick an AI into doing something it shouldn’t — like leaking data. A real risk as agents start reading the open web.

Jailbreak

Watch out

Trying to phrase a prompt so the AI ignores its own safety rules. Providers work hard to block it, and for any serious or regulated use, relying on jailbreaks is a liability, not a feature.

Bias

Watch out

When a model’s answers reflect skews in its training data — favoring some groups, views, or phrasings over others. Worth keeping in mind anywhere fairness matters.

Guardrails

Watch out

The rules and filters that keep an AI from producing harmful or off-limits output. Necessary, imperfect, and a big part of what separates a toy from an enterprise tool.

Shadow AI

Watch out

Employees using AI tools their employer hasn’t approved — usually free, personal accounts — often with company data. Widespread, invisible to IT, and the leading source of AI-related data leaks.

Example

Pasting a client contract into a personal ChatGPT account “just to summarize it.”

For builders

For anyone wiring AI into products, workflows, or internal tools.

API

Builder

A way for software to talk to an AI model directly, instead of a person typing in a chat box. It’s how companies build AI into their own apps and workflows.

Prompt engineering

Builder

The craft of writing instructions that consistently get good results from a model. Less about magic words, more about being clear and giving the right context.

Context engineering

Builder

The next step up — deciding what information to put in front of a model at each moment so it has exactly what it needs and nothing that distracts it. Crucial for building reliable agents.

Token cost

Builder

Since usage is billed per token, longer prompts and longer answers cost more. Trimming unnecessary context is how teams keep AI bills under control.

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