can search mah... this one been discussed to death here...
briefly:
omnibounce: plastic cap to spread flash all around a room for bounce. wun work if not walls to bounce. or too far off. "eats" colour of the walls.
diffuser: can't remember, think it's the pizza slice u attach to flash to bounce it, with a larger area. softens + weakens flash. bounce card is the diffuser.
