Deprimo is a charm which places immense downward pressure upon a target, which may cause the target to fracture.
Hermione Granger used this spell in 1998 to facilitate the escape of Harry Potter, and Ron Weasley, and herself from the Lovegood House. She blasted through a floor so that she, Harry, and Ron fell through, and then Disapparated them in the air.
Lord Voldemort also used a silent incantation on Harry Potter mixed with the Cruciatus Curse in Harry Potter and the Goblet Of Fire (1994) during their duel in the graveyard to make Harry bow.
Etymology
The incantation for this spell is most likely derived from the Latin deprimo, meaning "I press down" or "dig deep"