From French 'foyer' (hearth), from Latin 'focus' (fireplace) — originally the warm room with a fire in a theater.
An entrance hall or lobby, especially in a hotel, theater, or apartment building; the area immediately inside the front door.
From French 'foyer' (a hearth, a fireplace, the green room of a theater), from Vulgar Latin *focārium (a place for the fire), from Latin 'focus' (a hearth, a fireplace), probably of non-Indo-European (possibly Ligurian or Mediterranean substrate) origin. In French, 'foyer' meant the fireplace, then the room with the fireplace (the hearth room), then the warm room in a theater where actors and audience could gather during intermission. English borrowed it specifically in the theater sense
The word 'focus' in English originally meant 'hearth' — the center of the Roman household. Johannes Kepler borrowed it in 1604 to describe the point where light rays converge, because the hearth was where light and heat concentrated in a room. The foyer, the focus, and the act of focusing all