XLR

XLR connectors are mainly used for microphones and other audio signals, and are an industry standard for professional audio and related stage technology. The 3-pin version is most common by far, but 5-pin and 4-pin connectors are also in use today. XLR connectors are also available in a mini version, mainly used where the regular connector is too bulky, e.g. for wireless transmitters for actors’ stage microphones, and such.

The connector type has several unique advantages, which means that it is now used for non-audio uses, too.

One advantage is the locking latch, which means that XLR connectors can’t easily be pulled out by the cord, an essential feature indispensable on stages and other temporary installations where people are moving about. Another unusual aspect of XLR connectors is that XLR cables always have a male connector on one end and a female on the other, which makes them easy to extend without special adapters. This also means that a user can't connect two outputs together – the male connector is used for signal out, while female is used for signal inputs. 

The fact that the XLR connector is so common also provides logistical advantages: it is easy and cheap to obtain cables in many different lengths and designs. 

Some examples of areas of use outside of audio are, for example, DMX signals (i.e. digital control of stage lights), pyrotechnics, AES/EBU (digital audio), and for charging  batteries in many electric bicycles, wheelchairs and electric scooters.