In computing, evdev (for event device) is a component of the Linux kernel for handling input (from keyboards, mice, joysticks, etc.) and a closely related input driver for both the X.Org Server and Wayland compositors. The kernel component is glue code which translates input events from peripheral-specific drivers into a generic structure which the input driver can easily translate into X11 events. Thus every input device with a Linux driver is compatible with the X.Org input driver, making X.Org much easier to configure.
Using evdev makes it easier for the X.Org server to support hotplugging of input devices and allows advanced input devices, like multi-button mice and multimedia keyboards, to work correctly. The previous approach involved a kernel-level sink device emulating a PS/2 mouse and an AT keyboard, which collected events from all input devices, while the X server was configured for one keyboard and one mouse.