A microcontroller, or MCU (microcontroller unit), is a small computer built on a single integrated circuit. One chip holds one or more processor cores, a small amount of RAM, program memory such as flash, and programmable input/output peripherals, so it can run a dedicated program without separate memory or interface chips.
Unlike the general-purpose microprocessors in personal computers, microcontrollers are designed for embedded jobs: car engine control, remote controls, appliances, power tools, toys, implantable medical devices and Internet of Things sensors. Many draw only microwatts while waiting for an input such as a button press, which suits battery-powered devices. Texas Instruments’ TMS 1000, commercially available in 1974, is often credited as the first microcontroller.
Source: Wikipedia, Microcontroller
Image: Microcontrollers Atmega32 Atmega8 by Vahid alpha, CC BY 3.0, via Wikimedia Commons.