What is the meaning of 321 jump

321 Jump is a kind of instruction which means to perform the next action together after counting 3, 2, 1. This instruction is widely used in various games, such as square dances and children's songs. The dances about 321 are:

1. Korean girl group GFRIEND's "3, 2, 1" is the main song in the regular first album "The Awakening", and the dance expresses the young girls' brave expression of love.

2. "321" is a duet dance from the United States featuring male contestant Tony and female contestant Jessica.