From The Collaborative International Dictionary of English v.0.48 :
Touchback \Touch"back`\ (t[u^]ch"b[a^]k`), n. (Football)
The act of touching the football down by a player behind his
own goal line when it received its last impulse from an
opponent; -- distinguished from safety touchdown.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
touchback
n 1: (American football) a play in which the opposing team has
kicked the football into your end zone