"Arduino hardware is an open-source circuit board with a
microprocessor and input/output (I/O) pins for communication and
controlling physical objects (LED, servos, buttons, etc.). The
board will typically be powered via USB or an external power supply
which in turn allows it to power other hardware and sensors.
Arduino also has an open-source software component which is
similar to C++. The Arduino integrated development environment
(IDE) allows you to write code, compile it, and then upload it to
your Arduino for stand alone use in prototyping and projects.