Four concentric squares (one inside the other). Square 1 is the inner square (with heads and sides); Square 2 is next outward, then Square 3 and the outer square is Square 4. Dancers are referred to as "ones", "twos" etc. depending on the square they belong to.
Gloria Roth 1974
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.