Meter in music refers to a continuous pattern of beat stresses. A time signature is used to denote the meter throughout the duration of a musical work or section. MIXED METERS involve placing a different time signature at the beginning of each measure, resulting in an irregular rhythmic feel.

 

Mixed meters consisting of time signatures that repeatedly alternate will oftentimes be grouped together at the beginning.

 

An example of mixed meters:

When counting mixed meters, the easiest and most accurate way is to think of it as an overdrawn version of an additive meter:  a pattern of beats that subdivide into smaller irregular groupings.