Definition of mosquito for English Language Learners. : a small flying insect that bites the skin of people and animals and sucks their blood.
What it is: Small-cap stock refers to a company with a market capitalization (calculated by taking a firm's current share price and multiplying that figure by the total number of shares outstanding) near the low end of the publicly traded spectrum.
A commonly used benchmark to measure the performance of U.S. small-cap stocks is the Russell 2000 Index. Maintained by Russell Investments, the constituents in this index are evaluated each year.