AI agent
An AI agent is software that uses a large language model to decide which steps to take and which tools to call, such as searching a database, drafting a reply or updating a record, to complete a task. Unlike a chatbot, it acts as well as answers. Production agents need guardrails, logging and a clear path to a human when they are unsure.
Human in the loop
Human in the loop is a design where a person reviews, approves or corrects an AI system's output before it takes effect. It is used where a wrong action would be costly, for example sending money, changing a customer record or replying on a regulated topic.
Large language model (LLM)
A large language model is a neural network trained on large amounts of text to predict the next word, which lets it write, summarise, classify and answer questions. Claude, GPT, Gemini, Llama and Mistral are examples. On its own, a model knows only what was in its training data, which is why business systems connect it to their own documents and tools.
Retrieval-augmented generation (RAG)
Retrieval-augmented generation is a pattern where a system first retrieves relevant passages from your own documents, then gives them to a language model to write the answer. It lets the model answer from current, private information and cite its sources. When a RAG system gives a confident wrong answer, retrieval is the usual cause, not the model.
Chunking
Chunking is how documents are split into pieces before they are indexed for retrieval. Splitting on the document's own structure, such as sections, clauses or table rows, keeps related facts together. Splitting at a fixed size can separate a table from its header and make retrieval fail.
Embedding
An embedding is a list of numbers that represents the meaning of a piece of text, so that texts with similar meanings sit close together. Retrieval systems compare the embedding of a question with the embeddings of stored chunks to find relevant passages.
Vector database
A vector database stores embeddings and quickly finds the ones nearest to a query. Pinecone, Weaviate, Qdrant and pgvector, an extension for PostgreSQL, are common choices.
Hallucination
A hallucination is when a language model states something untrue or unsupported by its sources, with full confidence. It is reduced, not removed, by grounding answers in retrieved documents, requiring citations, and testing against known questions before each release.
Evaluation harness (evals)
An evaluation harness is a set of automated tests that scores an AI system's answers against expected results before a change ships. A good harness runs on every release, including prompt edits, and blocks the release if quality drops.
Golden set
A golden set is a curated list of real questions with checked, correct answers, used as the benchmark inside an evaluation harness. It is reviewed and extended as new failure cases appear.
Guardrails
Guardrails are rules and checks around an AI system that limit what it can say or do: blocking unsafe topics, redacting personal data, requiring citations, or stopping an agent from taking an action without approval.
Prompt injection
Prompt injection is an attack where text in a user message, web page or document tries to override an AI system's instructions, for example telling an agent to ignore its rules or reveal data. Defences include separating instructions from content, limiting which tools an agent may call, and testing with known attack examples.
Model router
A model router sends each request to the language model best suited to it, weighing quality, speed and cost. Simple requests can go to a cheaper, faster model and hard ones to a stronger model, without changing the application.
Token
A token is the unit a language model reads and writes, roughly three quarters of an English word on average. Model prices, speed and limits are all counted in tokens.
Context window
The context window is the amount of text a language model can take in at once, measured in tokens. A larger window lets the model read more retrieved passages, but retrieval still decides which passages it sees.
Fine-tuning
Fine-tuning is further training of an existing model on your own examples so it adopts a style, a format or a narrow skill. It changes how a model behaves; it is not the best way to give it new facts, which retrieval does better.
PII redaction
PII redaction is removing or masking personally identifiable information, such as names, phone numbers, ID numbers and addresses, before data is stored, logged or sent to a model.