Meter refers to the organization of time in music. A time signature defines the meter of a piece of music.
A time signature can be found at the beginning of a piece of music; you use a time signature to understand the rhythmic structure of a song. For example, a 4/4 time signature has four beats in every measure and gives a quarter note one beat.
Rhythm refers to the pattern of beats in music. Notes can be short or long, and the organization of these various note durations defines the rhythm of the piece.
When you can understand the rhythm and meter of a piece, you can emphasize certain notes to change the feel of a song. If you change the beats on which you accentuate a note, you can keep a song fresh and interesting.
Rhythm and meter are especially important for collaborating musicians. Talk to your ensemble about paying attention to meter and listening to rhythm. When everyone can hear the groove of the song, everyone will sound better.