Time signatures fall into two basic categories – simple time and compound time. Simple time is any time signature where the basic beat is divisible by two. E.g., in * , ^ , and % the basic beat is a quarter note, which may be divided in half to become two eighth notes per beat.
Any time signature where the basic beat is divisible by three (e.g., a dotted quarter note) is called compound time. The most common example of compound time is six eight time. Other examples of compound are _ and + . In each case, the basic beat is felt as a dotted quarter note which can be divided by three.