A harp is a a stringed musical instrument with the plane of its strings positioned perpendicular to the soundboard. Harps can be enchanted to be played without assistance.
History
1991-1992
During the 1991–1992 school year at Hogwarts, a harp was used by Quirinus Quirrell to prevent the three-headed dog Fluffy from waking up while Quirrell attempted to steal the Philosopher's Stone for Lord Voldemort.
1993
During their performance at the 1993 Welcoming Feast, the Hogwarts choir were accompanied by a harp.
1996-1997
A harp was stored in the Room of Requirement during the 1996–1997 school year.