Bar (music)
A bar or measure is used in writing music.  It is a way of organizing the written music in small sections. Each bar is a small amount of time.  Most music has a regular beat (or pulse) which can be felt.  Each bar usually has the same number of beats in it.  Music that feels like 1-2-3-4-1-2-3-4 will be divided into bars with four beats worth of music in each bar.