Duple Meter

Duple meter is defined as two beats per measure. These beats within the measure serve as “the framework within which rhythm is established and perceived” according to Grove Music Online. Accents (strong-weak) determine the meter of the piece. Because of this variance in the accents groups, some pieces that have four beats can also be interpreted as duple meter. These accents that determine the meter may be stated explicitly be implied through the music.
Most marches and dances, such as bourees and gavottes, are in duple meter due to the fact that most people have two feet. Also, popular music tends to be in duple or quadruple meter. Within duple meter, there are two more categories: simple duple and compound duple. Most marches that you listen to are good examples of simple duple, such as Pomp and Circumstance. Pieces that are simple duple are usually in 2/2, 2/4, or 4/4. An example of compound double would be “Take Me Out to the Ball Game.” If you listen, it should sound like two large beats subdivided into three smaller parts. Pieces in 6/8 are usually considered to be compound duple.

Tonal Harmony, Fifth Ed., Steven Kostka and Dorothy Payne, McGraw Hill