The micro:bit is stamp-sized circuit board, called a 'micro controller', in that you write programs on a laptop, tablet or smartphone and copy them over via a cable or Bluetooth to be run.
These programs can take full advantage of the micro:bit's I/O (input/output) features like a couple of push buttons, temperature sensor, tilt sensor, motion sensor, compass, bluetooth communications and a small 5 x 5 dot matrix display.