A surface to which stompboxes and other pedals are affixed. Because the pedals are at least semi-permanently mounted to the pedalboard, all necessary wiring (aside from a connection from the guitar and to the amp) can remain in place, along with a dedicated AC power supply (if desired), etc.
A pedalboard can range from a basic piece of wood to a complex unit with myriad audio and MIDI I/O options, and more.