XLR is a name for a specific style of locking connector. In most cases, when someone says XLR cable, they are referring to an audio cable with 3-pin XLR connectors. Most microphones and professional sound equipment have 3-pin XLR connectors, allowing easy interfacing between devices. Originally invented by Cannon, (thus sometimes called a "Cannon-plug"), in the 1930's. XLR.
For more, See the collaborative Article Connectors, XLR.