What is mixed meter in music?

Mixed meter is when one piece of music has multiple meters or time signatures during the piece. A simple example: A song's verse is in 4/4, but the chorus is in 3/4 time. However, mixed meter more commonly means that the meter changes frequently (often every measure) during a piece. In these cases, the lower number in the time signature usually remains constant. For example, the meter might change every measure from 3/8 to 6/8 to 5/8 to 9/8 to 12/8, etc.