Beatmixing

Beatmixing is a disk jockey technique of playing two songs at the same time so that the beats of one song occur at the same time as the other.
Beatmixing was invented in the late 1960s by Francis Grasso, who tried to keep people from leaving the dance floor between the songs. Initially he was looking for records with the same tempo, counting the tempo with a metronome. When the tempos didn't match, he was adjusting the pitch control on the turntable to bring the beats in sync. Rosie, a mixer built for him by Alex Rosner, let him listen to any channel in the headphones independently of what was playing on the speakers, allowing him to beatmatch the records by ear; this became the defining feature of DJ mixers.
Due to its increase in popularity, beatmatching and beatmixing are now considered basic techniques among DJs in electronic dance music genres, becoming standard practice in clubs to create a seamless mix through the night, even if there are multiple acts.

Beatmix or beatmixing however should not be confused with another term used in radio imaging. Radio imaging refers to any produced audio material sung or voice over used to identify a radio station. A radio imaging company in Seattle, Washington called ReelWorld used the term "beatmix" to refer to a type of imaging material in which a jingle, a voice over liner and audio clips are produced to blend on a song intro. The concept is still the same with DJ beatmixing.