Training data is the set of examples a system practices on before you use it. If the examples are invoices, the system learns what an invoice looks like. If the examples are only successful sales calls, it never learns what a bad call sounds like. The examples are the product.
Ask three things before you trust a model that learned from your files. Were people allowed to use those files for this purpose. Do the examples include the hard cases, not only the tidy ones. And who labeled them, because two staff marking the same email differently teach the system two answers. Bad examples do not average out. They become the habit.
Think of it this way: Training data is the school curriculum. If the curriculum is biased, outdated, or incomplete, the graduate will be too, no matter how smart they are.
A healthcare startup spent three months sourcing and cleaning labeled medical transcripts before touching a model. That work directly determined the ceiling on what the model could achieve.
A clinic wants a system to sort incoming referral letters. The training data is two years of letters, each marked urgent or routine by a coordinator. If the night shift marked everything urgent to be safe, the system learns that habit and the urgent queue fills up again.
Every supervised AI project needs labeled data. Invest in data quality before model selection. The best model trained on bad data will underperform a simple model trained on good data. You cannot skip data preparation. If you do not have sufficient, representative, and clean historical data for the task, no model architecture will compensate for that gap.
You do not need to pick a model from this page. RaftLabs starts from the job: the documents, the decision, and what a wrong answer costs. You see a working version before a large build. The related work on our side is Data engineering.
This sits with the other foundations terms on the glossary. The words under every AI conversation, from the model itself to the data it learned from. Worth reading next: Artificial Intelligence (AI), Machine Learning (ML), and Large Language Model (LLM).