A lecture hall was a building where lectures were given.
In 2369, during the return trip from a psychological conference to the USS Enterprise-D, a runabout with Deanna Troi, Jean-Luc Picard, Data and Geordi La Forge aboard encountered a series of temporal fragments. When one of those caused Troi to view the others as frozen in time, Troi wasn't sure about her experience and commented that there had been moments in the conference's lecture hall she thought time was standing still, too. (TNG: "Timescape")
When Koval asked Julian Bashir for a private discussion during a conference on Romulus in 2375, Bashir told him the lecture hall was empty, but Koval brought him elsewhere for an interrogation. (DS9: "Inter Arma Enim Silent Leges")
In 2376, Tincoo suggested The Doctor perform a concert in one of the lecture halls at the university on the Qomar homeworld, but The Doctor doubted a lecture hall would meet his acoustic requirements. The hall was then modified to meet his requirements. (VOY: "Virtuoso")