What's the difference between an undrafted free agent and a rookie minicamp tryout?
"The main difference is if you're an undrafted free agent, you sign your contract immediately," the agent said. "If you're getting invited for a tryout, you're not signing a contract. You're basically going out there with a two- or thee-day tryout and then they decide out of this pool of 15 or 20 guys they brought in, 'OK, we're going to sign this one or that one.' Then at that point, (tryout players) sign their contract as an undrafted free agent."
During rookie minicamps, teams provide players with food, lodging and a nominal per diem. Even during training camp, players receive relatively modest compensation: $1,075 per week for every rookie and $1,900 per week for every veteran.
The key for every NFL player is to earn a spot on the 53-man roster, because they are only paid their salary during the regular season. For every week a player is on the roster, he receives 1/17th of his salary ($27,352 for a player on a minimum contract).
"Teams want to bring the best players in and they put a priority on the guys that are more coveted. So they give them some signing bonus to entice them to sign with them," the agent said. "But as an agent, my advice is always seek the opportunity, not the short-term money. If a team is going to pay you $5,000 but you have a great chance to make a roster versus $20,000 and they've already got plenty of guys at that spot, you're not looking to make your money there."
http://www.nj.com/giants/index.ssf/2017/04/whats_the_difference_between_an_undrafted_free_age.html