Arduino is an open source hardware and software project, created with a simple aim in mind, to be as simple as possible. Arduino is not some hardware you should be afraid of. Arduino comes in a variety of flavors and sizes. It is used by artists, hackers, hobbyists, and professionals to easily design, prototype and experiment with electronics. Use it as brains for your robot, to build a new digital music instrument, or to make your house plant tweet you when it's dry. An Arduino contains a microchip, which is a very small computer that you can program. You can attach sensors to it so that it can measure conditions (like how much light there is in the room). It can control how other objects react to those conditions (room gets dark. LED turns on).
The project is based on microcontroller board designs, produced by several vendors, using various microcontrollers. Microcontrollers use inputs and outputs like any computer. Inputs capture information from the user or the environment while outputs do something with the information that has been captured. A switch and a sensor could be a digital and an analog input respectively into the Arduino. Any object we want to turn on and off and control could be an output. It could be a motor or even a computer. These systems provide sets of digital and analog input/output (I/O) pins that can interface to various expansion boards (termed shields) and other circuits. The boards feature serial communication interfaces, including Universal Serial Bus (USB) on some models, for loading programs from personal computers. For programming the microcontrollers, the Arduino project provides an integrated development environment (IDE) based on a programming language named Processing, which also supports the languages C and C++. The Arduino language is very similar to C. It's almost the same language but Arduino provides us with several libraries to make things a bit easier.
The first Arduino was introduced in 2005, based on 8-bit Atmel AVR, aiming to provide a low cost, easy way for novices and professionals to create devices that interact with their environment using sensors and actuators. Common examples of such devices intended for beginner hobbyists include simple robots, thermostats, and motion detectors.
Arduino comes in a variety of different boards. Arduino boards are available commercially in pre-assembled form, or as do-it-yourself kits. The hardware design specifications are openly available, allowing the Arduino boards to be produced by anyone. In mid-2011, it was estimated that over 300,000 official Arduinos had been commercially produced, and in 2013 that 700,000 official boards were in users' hands.