Training Data

Full definition

For supervised learning, training data consists of input-output pairs (e.g., images and their labels). For self-supervised pretraining of LLMs, it is typically trillions of tokens of web text, code, and books. Data quality — coverage, label accuracy, freedom from leakage — usually drives final model quality more than algorithm choice. The data-centric AI movement, popularized by Andrew Ng, codifies this: better data often beats better algorithms in enterprise settings.

Why it matters

In production AI projects, data collection, cleaning, and labeling take a large share of engineering effort. In RAND's 2024 interviews with 65 experienced data scientists and engineers, data problems were the second most common cause of AI project failure, after misunderstanding or miscommunicating the problem to be solved. Buyers should ask vendors not "what model did you use?" but "where did your training data come from, and how was it labeled?"

Example

A medical-imaging model trained only on adult X-rays performs poorly on pediatric scans — a training-data coverage gap, not an algorithm flaw.

Next steps

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Related terms

• Supervised Learning
  Supervised learning is the machine-learning paradigm in which a model learns from training examples paired with correct labels, then predicts labels for new, unseen inputs — the dominant approach in production ML today.
• Model Drift
  Model drift is the degradation of an AI model's performance over time as the data it sees in production diverges from the distribution it was trained on — the silent failure mode of every deployed ML system.
• AI Bias
  AI bias is systematic, unfair difference in an AI system's outputs across demographic, geographic, or other groups — usually caused by biased training data, biased labels, or biased problem framing rather than the algorithm itself.
• Fine-Tuning
  Fine-tuning is the process of further training a pretrained model on a smaller, task-specific dataset so it specializes in a particular style, domain, or behavior — without retraining from scratch.
• Synthetic Data
  Synthetic data is artificially generated training data — produced by AI models or simulators rather than collected from the real world — used to augment, replace, or supplement real datasets while preserving privacy or covering rare cases.

More fundamentals terms

• Inference
  Inference is the process of running a trained AI model on new, unseen inputs to produce predictions, classifications, or generated content — the part that runs every time a user interacts with the system.
• Model
  An AI model is the trained artifact — a specific set of numerical weights plus an architecture — produced when a learning algorithm runs against training data, and the thing that actually gets deployed and audited.