Definition: An unrestricted free agent may sign with any club, with no compensation owed to his old club, through the first scheduled day of the first NFL training camp (generally late July). At that point, his rights revert to his old club if it made a "tender" offer (110 percent of last year's salary) to him by June 1. His old club then has until the Tuesday after the 10th week of the season to re-sign him. If he does not sign by then, he must sit out the season.
If no tender is offered by June 1, the player can be signed by any club at any time throughout the season.
An unrestricted free agent must have completed four or more accrued seasons with an expired contract.