Arduino is an open-source electronics platform used to create interactive electronic objects. It consists of both a physical programmable circuit board (often referred to as a microcontroller) and a piece of software, or IDE (Integrated Development Environment) that runs on your computer, used to write and upload computer code to the physical board.
For example, you could use Arduino to create a robot that follows a line on the floor, or a device that turns on an LED when it senses motion. Arduino can also be used to control lights, motors, and other physical objects.