They are the same. In England and
much of Europe, these rides usually go clockwise. In the US
they move counterclockwise. To some Americans, a
merry-go-round is a simple spinning playground fixture for
children and a carousel is a more elaborate ride, with
music, fancy horses, and other creatures.
They both can be a revolving circular platform fitted with
seats, often in the form of animals, ridden for amusement,
or a piece of playground equipment consisting of a small
circular platform that revolves when pushed or pedaled.
Another definition of carousel is a tournament in which
groups of knights took part in chariot races and other
demonstrations of equestrian skills. Still one more is a
continuously revolving belt, track or other device on which
items are placed for later retrieval, such as a food or
luggage carousel.