A large, fluctuant, painless swelling of the floor of the mouth is shown. What is this?

A ranula is the classic name for this kind of large, fluctuant, bluish, painless swelling specifically in the FLOOR OF THE MOUTH, arising from the sublingual gland (a mucus extravasation phenomenon, sometimes called the 'frog belly' for its appearance). A typical mucocele is usually smaller and most often found on the lower lip, not specifically described as this large a floor-of-mouth swelling.