Arduino is an open-source hardware platform for building electronics projects. It was developed in 2005 in Italy to provide a simple tool for non-engineers to create digital projects. Popular Arduino boards include the Uno, Leonardo, Mega, and Nano. The Arduino uses an open-source IDE software to write code and upload it to the board, supporting programming languages like Processing. Key components of Arduino boards include a microcontroller, digital and analog pins, flash memory, and operating voltage of 5V.