Arduino is an open-source platform used for building electronics projects. An Arduino consists a circuit board and software (Integrated Development Environment) to program the board.
The Arduino platform is used as a starting platform. It is cheap, easy to use and there are many examples available to work from . The language that you use is a simplified version of C++, making it easier to learn to program. There are different sizes of Arduino some are very small and allow small enclosures or as an embedded element. Power consumption is low, it can run on battery power