Crown Moldings are ceiling trims that are placed between the wall and ceiling, the term 'molding' and 'trim' can usually be used interchangeably.
Where two walls meet each other, the crown molding will need to have a corner, and this would be referred to as a 'crown molding corner' or 'crown molding corner block', which is just another way of saying 'crown molding corner molding'. In short, they're the same thing, a crown molding that would be placed in the corner of a room, where two walls meet.