The AI Field Guide / R

Letter R

11 terms, explained without the techno-murk.

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Random forest

Deeper

A prediction method that combines the answers from many decision trees.

One tree can be swayed by quirks in its training data. A random forest grows many slightly different trees and lets them vote, like asking a crowd of varied advisers instead of trusting one.

For example

Hundreds of trees vote on whether a transaction looks fraudulent.

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Reasoning model

Newer term

A model designed to spend extra processing on multi-step problems before answering.

These models can perform better on difficult maths, code and planning tasks by using more inference-time work. They can still make mistakes, and a longer answer is not proof of better reasoning.

For example

A reasoning model explores several approaches to a logic puzzle before choosing an answer.

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Recommendation system

Everyday

A system that suggests items a person may find useful or interesting.

Recommendations may use past behaviour, similarities between people or features of the items themselves. They can be convenient, but they also shape what people see and may repeatedly narrow choices toward more of the same.

For example

A streaming service suggests films based on viewing history and patterns from similar viewers.

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Recurrent neural network (RNN)

Deeper

A neural network that carries information forward while processing a sequence.

Unlike treating every item separately, an RNN keeps a running note of what came before. This makes it useful for ordered data, although that note can fade across long sequences.

For example

An RNN uses earlier words in a sentence when processing the next word.

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Red teaming

Everyday

Deliberately trying to make an AI system fail so weaknesses can be found.

Testers probe for harmful outputs, security gaps, bias and unexpected behaviour. Red teaming helps reveal problems but cannot prove that every possible failure has been found.

For example

A team tests whether disguised instructions can trick an agent into sharing confidential files.

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Regression

Everyday

Predicting a number rather than choosing a category.

Classification answers 'which kind?'; regression answers 'how much?' or 'how many?'. It learns how input features tend to relate to a numerical result.

For example

A model predicts a home's selling price from its size, location and condition.

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Regularisation

Deeper

Techniques that discourage a model from becoming too complicated or memorising its training data.

It is like grading a student on clear general rules, not rewarding them for memorising every answer on one worksheet. A small constraint can help the model perform better on new examples.

For example

Training adds a penalty when model weights grow unnecessarily large.

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Reinforcement learning (RL)

Deeper

Learning by trying actions and receiving rewards or penalties.

The system learns a strategy that tends to produce more reward over time. Designing the reward carefully matters because an AI may find shortcuts that score well without achieving the real goal.

For example

A game-playing AI receives a positive reward for winning and learns which moves improve its chances.

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Reinforcement learning from human feedback (RLHF)

Deeper

Using human preferences as a signal to make a model's replies more helpful or acceptable.

People compare or rate model outputs, and that feedback helps train the system toward preferred behaviour. It reflects the examples and raters used, so it does not solve every alignment problem.

For example

Reviewers choose which of two answers is clearer and safer, helping shape later responses.

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Retrieval-augmented generation (RAG)

Everyday

Looking up relevant information and giving it to a generative model before it answers.

RAG helps a model use private or current sources without retraining. A search step finds useful passages, which are placed into the model's context. Poor retrieval can still lead to poor answers.

For example

A workplace assistant searches company policies, then answers with links to the matching documents.

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Robot

Start here

A physical machine that senses its surroundings and carries out actions.

Some robots follow fixed instructions, while others use AI to recognise objects, plan movements or adapt. AI does not need a robot body, and a robot does not necessarily use AI.

For example

A warehouse robot moves shelves by following routes and avoiding obstacles.

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