A two-point conversion is a play in American football which allows a team to attempt to score two points by running or passing the ball into the endzone instead of just kicking an extra point immediately following a touchdown. This is a rule currently present in professional, collegiate, and high school football. In college, the conversion is attempted from the 2-yard line, and in the NFL it is attempted from the 3-yard line. The Canadian Football League (CFL) places the attempt from the 5-yard line.
To quote from the NFL rulebook:
1. After a touchdown, the scoring team is allowed a try during one scrimmage down. The ball may be spotted anywhere between the inbounds lines, two or more yards from the goal line. The successful conversion counts one point by kick; two points for a successful conversion by touchdown; or one point for a safety.
The two-point conversion is mostly unchanged through various levels of play and is primarily seen in high school and college. It is especially prevelant in high school due to many teams not being able to dress or field an effective kicker, and in such a situation most coaches figure they might as well go for two points as opposed to still gambling on going for one. Some high school teams will go for the two-point conversion every time.
Most major college and professional coaches now carry a handy "2-point conversion cheat sheet" with them at all times to help them to decide when to only go for the extra point, and when to gamble and go for the two-point conversion. Each coach's sheet or card is customized by said coach to his or her tendencies to gamble -- some coaches are much more-likely to go for a win
than just to tie while others will almost always go the conservative route, for example.
The two-point conversion was in the rules for many years for the NCAA, most high school associations, and even the CFL. However the NFL only adopted the two-point conversion into its rulebook in 1994.