Crossover is the specific term for one type of checker movement: when it moves from one quadrant of the board to another, or when it is born off. It is important to note that a checker can move only to an adjacent quadrant. Not all the moves have specific terms in backgammon, only the ones of major importance and crossover is one of them.  Related term is crossover count, this refers to the total number of crossovers needed for getting all the checkers home and born them off.