The AI Field Guide / H

Letter H

6 terms, explained without the techno-murk.

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Hallucination

Start here

An AI answer that sounds plausible but is false, unsupported or invented.

Language models generate likely continuations, not guaranteed facts. They may invent names, quotations, links or events, especially when asked about uncertain or missing information.

For example

A chatbot confidently cites a court case that does not exist.

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Hidden layer

Deeper

A layer inside a neural network between the original input and the final output.

It is called hidden because people do not directly supply or read its values. Hidden layers build intermediate representations: in an image system, early layers might notice edges while later ones combine those clues into shapes and objects.

For example

Between a photograph entering the model and the label 'dog' coming out, hidden layers process increasingly complex visual patterns.

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Human evaluation

Everyday

People judging the quality, usefulness or safety of an AI system's output.

Human evaluation is useful when there is no single automatic test for qualities such as clarity, humour or helpfulness. Results depend on clear instructions and suitable reviewers; people can disagree or bring their own biases.

For example

Reviewers compare two summaries and rate which is more accurate and easier to understand.

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Human-in-the-loop (HITL)

Everyday

A design where a person reviews, guides or approves part of an AI process.

Human involvement is especially important when errors could affect money, rights, safety or reputation. It only helps when the reviewer has enough time, information and authority to intervene.

For example

An AI drafts a medical note, but a clinician checks and signs it before it enters the record.

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Hyperparameter

Deeper

A setting chosen for the training process rather than learned by the model itself.

Parameters are the model's learned notes; hyperparameters are the teacher's choices about how learning should happen. Examples include learning speed, batch size and number of training passes.

For example

A team tests several learning-rate hyperparameters to find one that trains steadily.

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Hyperparameter tuning

Deeper

Trying different training settings to find a combination that works well.

It is like adjusting oven temperature and cooking time before settling on the best recipe. The settings are not learned as ordinary model parameters, so developers test alternatives and compare their performance using separate validation data.

For example

A team compares several learning rates and model sizes, then keeps the combination with the best validation score.

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