Deliberately buying what most investors are selling, on the view that crowds overshoot in both directions. It needs a way to tell a genuine overreaction from a company that is falling for good reason, which is the entire difficulty. The losers list on the movers page and market breadth statistics are where a contrarian looks first, but the same rule as value investing applies: a cheap price is a question, not an answer.
See every term in the full PSE investing glossary.