3 stands for 3 beats, 4 stands for taking a quarter note as a beat, and 3/4 beats takes a quarter note as a beat, with 3 beats per bar, and there can be three quarter notes.

Related introduction:

In music, time is divided into equal basic units, and each unit is called a beat or a beat.

3/4 beats are mostly waltzes, and 2/4 beats are characterized by alternating strong and weak rhythms. When it is fast, there are often cheerful scenes. The 4/4 beat is a combination of 4/2 beats, and the second beat is diluted, thus making the song more lyrical.

Extended data

A whole note is equivalent to four beats, a half note is equivalent to two beats, an eighth note is equivalent to half a beat, and a sixteenth note is equivalent to a quarter beat; If the eighth note is taken as a beat, the whole note is equivalent to eight beats, the second note is four beats, the fourth note is two beats, and the sixteenth note is half beat.

When there is only one weak beat between two strong beats, it is called "double beat", and 2/4 beat is this type; When there are two weak beats between two strong beats, it is called "triple beat", like 3/4 and 3/8; There are three weak beats between two strong beats called "four beats"