College football is American football played by teams of student athletes fielded by American universities, colleges, and military academies, or Canadian football played by teams of student athletes fielded by Canadian universities. It was through college football play that American football rules first gained popularity in the United States.
Unlike most other sports in North America, no minor league farm organizations exist in American or Canadian football. Therefore, college football is generally considered to be the second tier of American football in the United States and Canadian football in Canada; one step ahead of high school competition, and one step below professional competition. However, in some areas of the country, college football is more popular than professional football, and for much of the early 20th Century, college football was seen as more prestigious than professional football.
It is in college football where a player's performance directly impacts his chances of playing professional football. The best collegiate players will typically declare for the professional draft after 3 to 4 years of collegiate competition, with the NFL holding its annual draft every spring in which 256 players are selected annually. Those not selected can still attempt to land an NFL roster spot as an undrafted free agent. - Source : MediaWiki