AVR313: Interfacing the PC AT Keyboard

What is a microcontroller?
A microcontroller or MCU is a computer-on-a-chip. It is a type of microprocessor dedicated to execute one task (as opposed to general purpose microprocessor), embedded in another device to control the features of that device thus, the name 'embedded controller'.

What is an AVR?
A voltage regulator is an electronic circuit used to maintain a level amount of voltage in an electrical line. It eliminates power surges, spikes and brownouts, which can cause harm to sensitive electronics.
AVR stands for automatic voltage regulator and is often used to refer to end-user equipment.