A time signature indicates the meter of a piece and consists of two numbers arranged like a fraction, the upper of which specifies how many beats are in each measure and the lower of which specifies the note value of each beat. It is placed in the staff for each instrument immediately after the clef and the key signature at the beginning of a score and again at any location where there is a change in either or both of its values.
The most frequently used time signature is 4/4, which means that there are four beats per measure and that each beat is a quarter note. It is referred to as common time and is often indicated by the capital letter 'C' in place of the numbers.