From a single file of two beside another single file of two (the files may face the same way or in opposite directions); also from Z-formation (from a wave have either the ends or the centers fold): The lead dancer in each file turns away from adjacent dancer ("Peels" away) and walks in a 180 degree arc to become the end of a regular or two-faced line. The trailing dancer steps forward and also peel away from adjacent dancer to walk in a very small arc 180 degrees and become the center of a regular or two-faced line. When both starting files face the same way, finishes in a regular line of four. When the two starting files are facing opposite to one another (4-person box or Z-formation), finishes in a two-faced line.
Howard Liffick 1962
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.