You probably will be hearing a lot about the waiver wire in the next few days so here is a simple reminder of how things work.
When teams make cuts, there are two different types, one for veterans and another for younger players.
Once players with more than four years of NFL service time are cut, they automatically become free agents. So Jeremy Ross, for example, is now free to sign with any team.
Players with less than four years of experience who are cut have to go through what are known as waivers. After such a player is cut, the other 31 teams are notified and are given a day to place a claim on that player. Essentially, claiming a player means the team will take his current remaining contract in full and give him a roster spot. If more than one team claims a player, he is awarded to the team that picked highest in the 2016 Draft (for now; early in the season the order becomes based on which team has the worst record).
If nobody claims a player, only then does he become a free agent and free to sign a new contract with another team or join a practice squad.
Today is the most active waiver day of the year because every team had to make around 20 cuts, primarily from young players with less than four years of experience.
For the Jets to fill out their practice squad, they will only be able to sign players who clear waivers.
If the Jets claim a player, somebody currently on the 53 man roster will need to be cut to clear room. This is why we say yesterday's roster was only the initial one. Further changes could be coming over the next few days as players are claimed off the waiver wire, and others are cut to make room.