Wiktionary
n. 1 (context American football English) The position at the end of the offensive line whose primary jobs are to block and serve as a short receiver. 2 (context American football English) A player playing the position of tight end.
WordNet
n. (football) an offensive end who lines up close to the tackle
Wikipedia
The tight end (TE) is a position in American football, Arena football, and formerly Canadian football, on the offense. The tight end is often seen as a hybrid position with the characteristics and roles of both an offensive lineman and a wide receiver. Like offensive linemen, they are usually lined up on the offensive line and are large enough to be effective blockers. On the other hand, they are eligible receivers adept enough to warrant a defense's attention when running pass patterns.
Because of the hybrid nature of the position, the tight end's role in any given offense depends on the tactical preferences and philosophy of the head coach. In some systems, the tight end will merely act as a sixth offensive lineman rarely going out for passes. Other systems use the tight end primarily as a receiver, frequently taking advantage of the tight end's size to create mismatches in the defensive secondary. Many coaches will often have one tight end who specializes in blocking in running situations while using a better pass catching tight end in obvious passing situations.
Offensive formations may have between zero and three tight ends at one time. If a wide receiver is present in a formation, but outside the tight end, the wide receiver must be positioned behind the line of scrimmage (see figure at right), since he is in the backfield, not on the line. If two tight ends are on the same side of the line of scrimmage, one must be behind the line of scrimmage, or the one not at the end of the offensive line has to report himself as non-eligible receiver. Also the offensive coordinator could use the tight end for a fullback.