Value investing is an investment strategy that deliberately overweights shares trading at low prices relative to a measure of the underlying business, in the judgment that the market has underpriced them. FINRA describes it as buying securities that, on fundamental analysis, are "trading below their intrinsic worth or at a discount to the market or their peers", and states the premise behind it: "if your holdings truly represent good value, the market will eventually adjust to reflect this."
A naming note, because two of our pages cover one subject. "Value stock" names the classification and "value investing" names the act of building a portfolio around it. The value stock page covers what the label means and how it fails; this page covers what running the strategy involves. Neither is the official term, because there is no official term: the strategy is described by regulators rather than defined by them.