A PICmicro microcontroller (Programmable Integrated Circuit) is a single chip microcontroller: a single integrated circuit containing a RISC processor, ROM, RAM, and I/O. You will use several microcontrollers every day: there is one in your watch, in your TV remote (and another in the TV), one in your burglar alarm, and probably several in your car. You can find microcontrollers in many different places.
PICmicro microcontrollers are becoming something of a standard in education because they are electrically reprogrammable, they are powerful, they are very low cost and they are simple to use. They allow you to easily design a single chip to perform a number of functions: to control a robot, to water plants in your greenhouse three times a day, for remote control encoding or for any number of other projects.
PICmicro microcontrollers themselves are available in a wide range of packages. From the small 8 pin DIL packages with just a few simple digital I/O lines, through to many-pinned surface mounted versions with multiple I/O lines, on board A/D converters etc.
For full details you should have a look at Arizona Microchip's web site at: www.microchip.com where you will find a host of information including all datasheets.
A PIC16F84 chip