This AI glossary explains the terms you will meet most often when using and choosing AI tools, in plain English. Knowing them makes it easier to compare tools, follow product announcements, and understand why AI behaves the way it does.
Part of Beginner Guides. Last updated September 2026.
Core Concepts
| Term | Plain-English Meaning |
|---|---|
| Artificial intelligence (AI) | Software that performs tasks needing human-like intelligence by learning from data |
| Machine learning | How AI systems learn patterns from examples |
| Large language model (LLM) | An AI trained on huge amounts of text to understand and generate language |
| Generative AI | AI that creates new text, images, audio, video, or code |
| Model | The trained AI system itself, such as a specific GPT, Claude, or Gemini version |
Using AI
| Term | Plain-English Meaning |
|---|---|
| Prompt | The instruction or question you give an AI |
| System prompt / custom instructions | Standing instructions that shape every response |
| Token | A small chunk of text; limits and prices are counted in tokens |
| Context window | How much text the model can consider at once |
| Hallucination | A confident answer that is false |
| Temperature | A setting that makes output more predictable or more varied |
| Multimodal | Able to work with more than text, such as images, audio, or video |
Building With AI
| Term | Plain-English Meaning |
|---|---|
| AI agent | AI that plans and carries out multi-step tasks using tools |
| RAG (retrieval-augmented generation) | Giving the model relevant documents to answer from, reducing made-up answers |
| Fine-tuning | Further training a model on specific examples |
| API | A way for software to use an AI model programmatically |
| MCP (Model Context Protocol) | An open standard for connecting AI assistants to tools and data sources |
| Embedding | A numeric representation of meaning, used for search and matching |
Frequently Asked Questions
What is a token in AI?
A small unit of text, often part of a word. Usage limits and API pricing are usually measured in tokens.
What does hallucination mean in AI?
When an AI produces information that sounds correct but is false or unsupported.
What is the difference between a prompt and a system prompt?
A prompt is your individual request; a system prompt or custom instructions set standing rules for every response.