In architecture, a penthouse is a building on the roof of another building, or alternatively, an apartment on the top floor of a building. See penthouse apartment.
Penthouse apartments are often expensive, and associated with a luxury lifestyle: this connotation was presumably the inspiration for the title of the pornographic magazine Penthouse.
This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. If an article link referred you here, you might want to go back and fix it to point directly to the intended page.