It is associated with the context of hip hop, but not necessarily limited to this genre.
Beat juggling can be defined as the art of manipulating two or more samples (e.g. drum beats, or vocal phrases), in order to create a unique composition, using multiple turntables and one or more mixers.
[1] This can involve pauses, scratching, backspins and delays.
Despite being a classical technique in deejaying and turntablism, beat juggling isn't limited to analogue mixing with vinyl records.
[2] The technique gained widespread popularity beginning in 1990.