Domain Knowledge

Domain knowledge is the understanding of a specific discipline, industry, or problem context that enables a practitioner to make judgments about which patterns matter, which assumptions are safe, and which simplifications are dangerous. In machine learning, domain knowledge is often treated as an inferior substitute for data — something to use only when training sets are small — but this framing inverts the actual relationship. Domain knowledge is the compression of centuries of observation, failure, and refinement into heuristics that no dataset, however large, can replicate. The claim that data can always substitute for expertise is a claim made by people who have never tried to model a process they do not understand.