Arduino is an open-source electronics platform based on easy-to-use hardware and software. Arduino boards are able to read inputs - light on a sensor, a finger on a button, or a Twitter message - and turn it into an output - activating a motor, turning on an LED, publishing something online. You can tell your board what to do by sending a set of instructions to the microcontroller on the board. To do so you use the Arduino programming language (based on Wiring), and the Arduino Software (IDE), based on Processing. (Source)
![Arduino Uno](https://store-cdn.arduino.cc/usa/catalog/product/cache/1/image/500x375/f8876a31b63532bbba4e781c30024a0a/a/0/a000066_front.jpg)