As such sidechaining is not new, but the exaggerated effect has become quite popular in Dance music - the characteristic pumping sound is achieved with this technique. A very common application is to sidechain a compressor or gate in order to avoid that multiple sounds in the same frequency range clash, for instance the kick drum and bassline. Sidechaining is the technique where one sound is used to affect another.
FL Studio 9 tutorial explaining sidechaining.
