Xtended Locking Round. Developed by ITT/Cannon, XLRs are rugged, locking, multi-pin connectors frequently used in pro audio equipment. While 3-pin XLRs are most commonly seen on microphones and console inputs, other configurations also exist, such as 4-pin XLRs (a standard for stage intercom systems) and 5-pin XLRs (often used on stereo microphones). A designation of “M” after the pin number, such as “XLR-3M” indicates a male connector. Sometimes also called a Cannon connector.