Is a microcontroller make by Microchip corporation.
And the PIC distiguish for the rest is because is a product of Microchip(www.microchip.com) and not of atmel, lattice, maxim or motorola(freescale).
The PIC microcontroller has the same periphericals (pwm, adc, port in, port out) of the rest microcontrollers like the AVR,TINI, etc, The only thing that make the different is if you like or not to use it in you project.
PIC stands for Peripheral Interface Controller. Originally it was designed as coprocesser. Later became stand alone controller and now have very powerfull derivatives.
From what I've been learning about them they're also signifigantly cheaper than most other brands. The lowest end PIC's are about USD0.75 a piece and even the more powerful 16 bit ones rarely breach $5.00 a piece.
PIC Microncontroller is a powerful MCU that is dominating other MCUs..these are small but powerful MCU that uses only intructions that can be easily manipulated!
for more knowing about pic microcontroller i highly recommended some books are already on edaboard such as:
PICC
PIC project book
Basic for PIC microcontroller