The beat is the basic unit of musical rhythm. In other words, it is the note value used for counting – most often half-, fourth-, and eighth notes. It's vitally important that the recurring beat, or pulse, is felt in the body and is present at the back of the mind when playing music or listening to it critically.
In most music, beats fall into regular groups of twos or threes or of combinations of these (as a group of 4 made up of 2+2, or a group of 6 made up of 3+3). Such groups or combinations of groups are indicated by the drawing of bar lines at regular intervals, so dividing the music into bars (or measures). The base counting value and the number of them in each bar is indicated at the start of the music by the time signature.
The first beat in a bar is called the downbeat, a term that comes from orchestral conducting, where the lowest point as the baton comes down signals the first beat in the measure. In 4/4 time, the bass drum is often used to play beats 1 and 3, while the snare drum snaps on beats 2 and 4 (the backbeats).
Beats per minute (bpm) is a measurement of the tempo of a piece of music. Most music has a tempo of 60–220 beats per minute.