The Quad

It’s short for “quadrangle,” which is the shape it was originally when it was a courtyard inside a building. If a courtyard is surrounded by rectilinear buildings, then it’s going to form a rectangle of some kind.

Some universities have gathering places that are no longer enclosed (or even rectangles), but, over time, “the quad” has become a general idiom for central gathering place of a campus.

One resource claimed that Merton College was the first to have an area called a “quad.” Here’s the satellite view and you can see that the university has many courtyards that are squares or rectangles of some kind. Some labels I noticed: Mob Quad, St. Alban’s Quad, and Tom’s Quad.

There’s a Wikipedia page for Quad which mentions universities specifically, and also calls out cloisters in religious buildings – the “quads” in those buildings are often surrounded by open hallways.