As the name implies, instrument audio cables are used between musical instruments, e.g. electric guitars or microphones, and associated effects pedals, amplifiers, mixing consoles etc.
Between instruments, microphones and mixers (or active speakers), balanced XLR cables are the most common, but 6.3 mm Jack cables are also widespread.
For wireless microphones, Mini XLR cables are often used between the microphone and the transmitter (microport). From the base to the amplifier, regular XLR cables are normally used.
XLR cables can also be used as control cables for DMX-controlled lighting and effect equipment and machinery, with either 3- or 5 pin XLR connectors.