A checker is someone who examines or verifies something to make sure it's correct or complete. In a grocery store, the checker is the person who scans your items and totals up what your family owes. They're checking that everything gets counted properly. Before turning in an essay, you might ask a friend to be a checker and look for spelling mistakes you missed.

The word also refers to one of the round, flat game pieces used in the board game checkers. Each player starts with twelve checkers on opposite sides of the board, moving them diagonally across red and black squares. When you jump over an opponent's checker, you capture it and remove it from the board. If your checker reaches the opposite end of the board, it becomes a king and gains the power to move backward as well as forward.

Less commonly, checker describes a pattern of alternating squares in two colors, like a checkerboard or a checkered flag waved at the end of a race. A checkered past means someone's history includes both good and bad periods, like squares of different colors on a board.