From eight chain thru formation: Center couples will do a full Square Thru (half of it with the couple they face and the last half with the couple coming across from the other side). Outside couples do an eight chain two and then half Square Thru with the couple on the opposite side of the square. Finishes in lines facing out.
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.