Question

Training data vs evaluation data: what's the difference?

By SourceX Editorial · Updated October 2, 2026

Short answer

Training data is used to teach a model — adjusting its parameters — while evaluation data is held back to measure how well the model performs. Training sets are usually larger; evaluation sets are smaller but must be high quality, representative and kept separate from training to give honest results. Both can be licensed, and evaluation licenses often restrict use to testing only.

Part of: AI evaluation data

Comparison

	Training data	Evaluation data
Purpose	Teach the model	Measure performance
Size	Larger	Smaller
Key requirement	Volume and relevance	Quality and separation
Typical licence	Training use	Testing use only

Explanation

Evaluation data must not leak into training, so buyers often require exclusivity or strict separation.

Expert-verified answers make evaluation data especially valuable.

Rights and privacy

Evaluation-only licenses may prohibit training use
Confidentiality to prevent contamination

How licensing works

A business describes its data, buyer demand is assessed, scope and permitted use are proposed, the data is prepared and de-identified, an agreement is signed, and the approved dataset is delivered. See data licensing for detail.

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