A measure is a measurement or division of time in music. It is sometimes also called a Bar. In 4/4 time there are 4 beats or pulses to the measure, in 3/4 there are 3 beats or pulses in a measure. Tempo is the speed at which the measure passes by, fast tempo, slow tempo, medium tempo etc. These are sometimes marked with metronome markings to establish exact measure lengths. Measures help to establish song form and generally make music easier to read and communicate no matter what the style or whether or not the music is written down.