The term Tower in the Harry Potter series most commonly refers to one of the numerous spires that comprise the silhouette of Hogwarts Castle. These towers serve a variety of functions, housing classrooms, the Headmaster's office, the common rooms and dormitories for three of the four Hogwarts houses, and other specialized areas such as the Owlery. The towers are key locations for many pivotal events in the narrative.
The Astronomy Tower
Gryffindor Tower
Ravenclaw Tower
The North Tower
The West Tower