A match is a contest between players in which a number of games is played to determine a winner.
Common formats, often used in finals of big titles, are best-of-three, best-of-five and best-of-seven. With non-integer komi like 6.5 or 7.5, an odd number of games guarantees a winner, as ties are impossible.
In the days before komi, playing a match of multiple games was also used as a way to offset the starting advantage that black has. In a match between evenly matched opponents, an even number of games without komi is more fair, as that way both can have the starting advantage an equal number of times.