Players who are not drafted in a league’s annual draft of amateur players are considered to be unrestricted free agents and are free to negotiate contracts with any team.
In most American professional sports, players are drafted by sequencing each team from worst to best (according to the team’s win-loss records the previous season, sometimes invoking a draft lottery factor to avoid having teams intentionally lose their last games to gain higher draft position) and allowing said teams to claim rights to the top players entering the league that year.
Players that pass through an entire draft (usually several rounds) without being selected by any of the league’s teams become unrestricted free agents, and these players are sometimes identified simply as an undrafted free agent (UDFA) or undrafted sportsperson and are free to sign with any team they choose.
The term “undrafted free agent” is most common in the National Football League (NFL), where rookies enter directly into the NFL and do not play in a minor league system.
It can also occasionally be seen in the National Hockey League (NHL), which increasingly uses college hockey as a source; the NHL Entry Draft usually drafts players during high school age (i.e., junior leagues), which allows overlooked players who excel at the college level or in European professional leagues to bypass the draft and sign directly with the NHL.