From Trade By formation: Those facing out Cross Cast Back and move ahead to Slide Thru with the one from the other side. Center four Fan the Top and Step Thru. Finishes in eight chain thru, completed double pass thru or some other formation depending upon the sex facings for the Slide Thru.
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.