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AI Glossary: 25 Essential Terms (2026)
New to artificial intelligence? This glossary covers the 25 most important AI terms you'll encounter in 2026. Each definition is concise, clear, and updated for the latest AI landscape.
Artificial Intelligence (AI)
Computer systems that perform tasks typically requiring human intelligence — reasoning, learning, pattern recognition, language understanding.
Large Language Model (LLM)
AI models trained on massive text datasets to understand and generate human language. Examples: GPT-4, Claude, Gemini.
ChatGPT
OpenAI's conversational AI assistant launched in November 2022, built on the GPT family of language models.
Claude
Anthropic's AI assistant, known for its strong reasoning capabilities, constitutional AI training, and long context windows.
Gemini
Google's multimodal AI model family, capable of processing text, images, audio, and video.
Transformer
Neural network architecture introduced in 2017 ('Attention Is All You Need') that powers most modern language models.
Reinforcement Learning from Human Feedback (RLHF)
Training technique where models learn to align with human preferences through feedback loops.
Prompt Engineering
Crafting input prompts to get optimal outputs from language models. A key skill for working with AI.
Token
Basic unit of text that LLMs process. Roughly 4 characters or 3/4 of an English word.
Context Window
Maximum amount of text an LLM can consider at once. Modern models range from 8K to 1M+ tokens.
Multimodal AI
AI systems that process multiple types of data (text, image, audio, video) simultaneously.
Fine-tuning
Adapting a pre-trained model to specific tasks or domains by training on specialized data.
Hallucination
When an AI generates plausible-sounding but factually incorrect information.
Agent / Agentic AI
AI systems that can autonomously plan and execute multi-step tasks using tools.
RAG (Retrieval-Augmented Generation)
Technique where LLMs query external knowledge before generating responses, improving accuracy.
Embedding
Vector representation of text/data that captures semantic meaning for similarity search and ML tasks.
Mixture of Experts (MoE)
Architecture where different parts of a model specialize in different tasks, improving efficiency.
Open Source AI
AI models with publicly available weights and code. Examples: Llama, Mistral, Stable Diffusion.
AI Alignment
Research field ensuring AI systems pursue intended goals safely and beneficially.
AGI (Artificial General Intelligence)
Hypothetical AI matching human intelligence across all cognitive domains.
AI Safety
Field focused on preventing harmful AI behaviors, both near-term and existential risks.
Inference
Process of running a trained AI model to produce outputs on new inputs.
Training
Process of teaching an AI model by exposing it to large datasets and adjusting parameters.
Foundation Model
Large pre-trained model that serves as a base for many downstream applications.
Constitutional AI
Anthropic's training approach using principles to guide AI behavior without constant human feedback.
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