Arduino is an open source electronics prototyping platform.

It is based on flexible hardware and software and is concerned with interactive objects and environments.

"Physical computing, in the broadest sense, means building interactive physical systems by the use of software and hardware that can sense and respond to the analog world.  Physical computing is a creative framework for understanding human beings' relationship to the digital world. In practical use, the term most often describes handmade art, design or diy hobby projects that use sensors and micro controllers to translate analog input to a software system and/or control electro-mechanical devices such as motors, or other hardware."