A cable used to split or combine two signals. Another use is to send a signal out of one side of the "Y" and return through the other, as when patching into an insert point of a console. There are occasions where "Y" cables should not, or cannot be used. One is for MIDI. It is impossible to combine two channels of MIDI using a "Y" cable. Combining two outputs of an amplifier is also not something that should be done. In general, "Y" cabling should be avoided except in the send/return scenario, or with propriety cables, such as Digidesign's MH069 cable, used for connecting two interfaces to a single DSP card.