http://www.explore-football.com/football/O/Offensive_team.html
tight end - tight ends play on either side of, and immediately next to, the tackles. They are a mix between a blocker and a pass receiver. If an end moves away from the tackle, he is called a split end. Modern formations typically have one end tight, the other split. Many modern formations dispense with tight ends completely, replacing them with wide receivers. Sometimes a formation is referred to as having "three tight ends", which in reality means an additional blocker (a wingback or an eighth lineman) has substituted for a wide receiver, as in short-yardage situations.
fullback - positioned behind the middle of the line, a fullback may do some running, some blocking, and some short receiving. A classic fullback is more of a straight-ahead, "four yards and a cloud of dust" power runner than a halfback. Many modern formations do not use a fullback. Most plays utilizing the fullback call for him to block, generally by running up the middle of the line, clearing a path for a running back to use.
running back - the modern term for the position formerly called "halfback". "Fullback" is now regarded as a separate position from running back, with a substantially different role (especially in the NFL).
tailback - a running back that is positioned behind the middle of the line and deepest of all backs.
H-back - a position that was popularized by Joe Gibbs during his first tenure with the Washington Redskins; the H-back is a hybrid position that combines the skill sets of fullback, tight end, and even wide receiver. An H-back lines up similarly to a wingback, but deeper and not as wide, and frequently serves as a blocker for a more deeply positioned back.
wingback - a player positioned just outside of behind the outermost lineman who is not split from the rest of the line; if no linemen are split, then the wingback position is just outside of and behind the (tight) end.