General-purpose input/output (GPIO)

Random board with a STM32 MCU

A general-purpose input/output (GPIO) is an uncommitted digital signal pin on an integrated circuit or electronic circuit board which may be used as an input or output, or both, and is controllable by the user at runtime.

All STM32 MCUs have a high number of GPIOs. In fact, almost all pins on a MCU package, which is not dedicated a power pin are GPIOs:

The GPIOs are divided into a number of ports (the actual number depends on the pins available on any particular package) labelled with letters and starting with "PortA".