* The Great Square of Pegasus: This is the most likely answer. It's a prominent asterism (a recognizable pattern of stars) within the constellation Pegasus, forming a near-perfect square. It's composed of the stars:
* Alpheratz: Alpha Andromedae
* Scheat: Beta Pegasi
* Markab: Alpha Pegasi
* Algenib: Gamma Pegasi
* Other Square-shaped Patterns: There are other less well-known square-like shapes in the sky, but they aren't widely recognized as "Square" constellations:
* The Square of Ursa Major: The four stars at the end of the "Big Dipper" bowl form a rough square.
* The Square of Corvus: This is a smaller square-shaped asterism within the constellation Corvus (the Crow).
If you can give me more context about where you heard the term "Square" constellation, I might be able to give a more specific answer.
