The result of a play (usually a kickoff or punt) in which the ball passes out the back of the end zone or a team otherwise gains possession of the ball in their own end zone.
The ball sailed into the end zone for a touchback and the Eagles had possession on the 20-yard line. https//web.archive.org/web/20060111202354/http://www.philadelphiaeagles.com/gameday/postGameArchive.jsp?id=16746