AI Glossary: 30 Terms Explained in Plain Language

Updated 2026-10-25 · 10 min read · AI Tools World editorial team

AI product pages are full of jargon. This glossary explains the terms you will see most often in plain language, so you can understand what a tool actually does before you pay for it.

Artificial intelligence (AI)

Computer systems that perform tasks normally associated with human thinking, such as understanding language, recognising images or making predictions.

Machine learning

A way of building AI where a system learns patterns from examples instead of following hand-written rules.

Generative AI

AI that creates new content — text, images, audio, video or code — rather than only classifying or predicting.

Large language model (LLM)

A model trained on very large amounts of text that can understand and generate language. ChatGPT, Claude and Gemini are built on LLMs.

Model

The trained system that produces answers. One product may offer several models with different speed, cost and capability.

Prompt

The instruction or question you give an AI tool.

System prompt

Hidden instructions a product gives the model to shape its behaviour, such as tone or rules.

Token

A small piece of text (often part of a word) that models read and write. Usage limits and API prices are usually counted in tokens.

Context window

How much text — your prompt, files and the conversation so far — a model can consider at once.

Hallucination

When an AI states something false or invented as if it were true.

Grounding

Connecting an AI's answer to trusted sources, such as search results or your documents, to reduce hallucinations.

RAG (retrieval-augmented generation)

A technique where the system first searches documents for relevant passages and then writes an answer based on them.

Fine-tuning

Further training a model on specific examples so it performs better on a particular task or style.

Multimodal

Able to work with more than one type of input or output, such as text, images, audio and video.

Text-to-image

Generating a picture from a written description.

Text-to-video

Generating a video clip from a written description or an image.

Text-to-speech (TTS)

Turning written text into spoken audio.

Speech-to-text

Transcribing spoken audio into written text.

Voice cloning

Creating a synthetic voice that sounds like a specific person. It should only be done with that person's consent.

Inpainting

Editing or replacing part of an image while keeping the rest.

Upscaling

Increasing the resolution of an image or video using AI to add detail.

AI agent

An AI system that can plan and carry out multi-step tasks, often by using tools such as a browser, files or other apps.

Copilot

A general name for AI assistants that work inside another product, such as a code editor or office app.

API

A way for software to use an AI model programmatically. Developers pay per use, usually by tokens.

Open-weight model

A model whose trained weights are published so others can run or adapt it, subject to its licence.

Inference

The act of a trained model producing an output from an input — what happens each time you send a prompt.

Benchmark

A standard test used to compare models. Benchmark scores do not always reflect performance on your own tasks.

Bias

Systematic unfairness in AI outputs, often inherited from training data.

Watermark

A visible or hidden marker showing content was AI-generated or created on a free plan.

Credits

Units many AI tools use to measure and bill usage, especially for images, video and audio.