The NFL’s free agency period officially opens Wednesday at 4 p.m. EST.

The two-day negotiating period for potential unrestricted free agents began Monday, giving teams permission to enter contract negotiations with players and sign them new contracts once the free-agency period officially opens.

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Several players have reportedly agreed to contracts, including Tom Brady, Philip Rivers and Drew Brees. Several players remain unsigned, including Jadeveon Clowney, Chris Harris and Yannick Ngakoue.

Here are some things to know about this year’s free-agent period.

WHAT IS A RESTRICTED FREE AGENT?

J.D. McKissic is among the restricted free agents this year. (Photo by Joel Auerbach/Getty Images)

A restricted free agent is a player with three or fewer accrued seasons who has received a tender from their current team. The player can negotiate with a club up to a certain date (for the 2020 season the deadline is April 17).

Should the player receive an offer from another team, their current club has five days to match the offer and retain him. If they don’t match, then the new team must give up draft picks in order to acquire the player.

WHAT IS AN UNRESTRICTED FREE AGENT?

Tom Brady is an unrestricted free agent in 2020. (Mark J. Rebilas-USA TODAY Sports)

A player becomes an unrestricted free agent after a player with four or more accrued seasons has their contract expire. The player is free to sign with any club through July 22 or the first day of training camp, whichever is later. After that date, the player’s negotiating rights revert back to their old club if by May 4 the old club tendered the player a one-year contract for 110 percent of his prior year’s salary.

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According to the NFL, the player’s “old club then has until the Tuesday following Week 10 of the regular season (November 17) to sign him. If he does not sign by that date, he must sit out the season. If no tender is offered by May 4, the player can be signed by any club at any time throughout the season.”

WHAT IS THE FRANCHISE TAG?

The Ravens placed the franchise tag on Matthew Judon. (AP Photo/Nick Wass)

An NFL team can use the franchise tag on one player only. The tag binds the player to the team for one year and depending on the offer the tag is considered to be an exclusive, or non-exclusive.

The franchise tag binds a player to the team for one season and their salary is based on the top five salaries at their position.

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An exclusive franchise player is not free to sign with another club and is offered the average of the top five salaries at the player’s position for the current year as of the end of the restricted free agent period.

A non-exclusive franchise player can negotiate a contract with any club but the potential new club must give up two first-round draft picks if he signs. The non-exclusive salary is determined by “summing the amounts of the Franchise Tags for players at that position for the five preceding five league years; dividing the resulting amount by the sum of the Salary Caps for the five preceding league years; and multiplying the resulting percentage by the Salary Cap for the upcoming league year; or 120 percent of his prior year salary, whichever is greater.”

WHAT IS THE SALARY CAP SET AT?

The 2020 salary cap is set at $198.2 million.