A form of adapter cable that passively splits the output of a source to feed two or more destinations.
Y-leads may also be used in unbalanced console insert points, in which case a stereo jack plug at one end of the lead is split into two monos at the other for separate send and return connections. A Y-lead must never be used to combine signals.
A simple 'Y-lead' (an insert send/return cable with a TRS connector on one end and dual TS connectors on the other) is all that's needed to connect a stereo headphone socket to two mono inputs of an audio interface or other recording device.