The XLR connector is an electrical connector design. XLR plugs and sockets are used mostly in professional audio and video electronics cabling applications, for microphones and line level signals. Home audio and video electronics normally use RCA connectors for line level signals generated by a preamplifier. Phone plugs are also used for microphones in home and computer applications.
In reference to its original manufacturer, James H. Cannon, founder of Cannon Electric in Los Angeles, California (now part of ITT Corporation), the connector is colloquially known as a cannon plug or cannon connector. Originally the "Cannon X" series, subsequent versions added a Latch ("Cannon XL") and then a Rubber compound surrounding the contacts, which led to the abbreviation XLR.[1] Many companies now make XLRs. The initials "XLR" have nothing to do with the pinout of the connector. XLR connectors can have other numbers of pins besides three.
They are superficially similar to the older and smaller DIN connector range, but are not physically compatible with them.

NOTE: Digital XLR
AES/EBU. Audio Engineering Society/European Broadcasting Union. AES/EBU is one of the common names for a digital audio transfer standard. The standard is also known as XLR because the AES/EBU digital interface is usually implemented using 3-Pin XLR connectors, which happens to be the same type connector used in a professional microphone. One cable carries both left and right-channel audio data. AES/EBU is an alternative to the S/PDIF [Sony/Philips Digital Interface] standard. S/PDIF is a an audio transfer file format which uses an RCA connector.

TRS connector
RCA jack
DIN connector
RF connector