Wikipedia
Oversigning (also spelled Over-signing) is an unofficial term for the practice of American college athletic departments signing prospective student-athletes to a National Letter of Intent (NLI) that may exceed the maximum number of athletic scholarships permitted by the National Collegiate Athletic Association (NCAA). The NCAA limits the total number of scholarships that may be awarded in all of its sponsored sports, and in football also limits the number of scholarships awarded in a given year. Those limits differ by sport and the division in which that school participates. Most conferences have additional rules governing signing NLI.
NCAA Bylaw 15.5.6.1 limits FBS football programs to a total number of scholarships to 85 "counters" annually including 25 scholarships for "initial counters." Counters (NCAA Bylaw 15.02.3) are individuals who are receiving institutional financial aid that is countable against the aid limitations in a sport, initial counters (NCAA Bylaw 15.02.3.1) are individuals who are receiving countable financial aid in a sport for the first time. Bylaw 13.9.2.3 limits schools to signing 28 NLI from initial signing day through May 31.
Oversigning can occur in two ways. First, if a school signs a number of NLI that may bring their total number of counters above the NCAA limit of 85. Second would be to sign more than 25 NLI during the period between National Signing Day and May 31.
Oversigning occurs in other sports but has received the most attention from media members and fans, in regard to Division I FBS college football.
NCAA rules permit oversigning up to 28 NLI, though some college football fans view oversigning as unethical, arguing that it requires schools and coaches to be dishonest with young adult and adolescent recruits by promising them a roster spot and scholarship only to pull it before the person graduates or even makes the team.