The past two seasons the NFL opened added two spots to each team's 8-man practice squad, bringing the number of practice squad players to 10. That new rule was up for extension this offseason and the NFL and NFLPA have mutually agreed to keep the number at 10 for at least another two seasons, according to ESPN's Mark Dominic.
With the initial practice squad expansion, the additional two spots could be filled by players with two accrued NFL seasons. All others were not allowed to have an accrued NFL season (more than 8 games active). The new deal will double the number of players who may have two accrued seasons from 2 to 4.
These rules are great for players as well as teams. The teams can keep more guys around to help the active roster as well as be familiar with the team's system so they may be called up at a moment's notice should the need arise. Opening more spots to players with up to two accrued seasons means they won't have to make sure they keep their practice squad hopefuls under a certain number of active games for fear of not being able to replace them on the practice squad later.