As promised, I'll go over some more rules during August. Today, the 50-contract rule.
Every NHL team wants depth in order to deal with injuries and develop players. But teams are limited in the number of players they can sign to contracts per year to just 50. Over half of those 50 can't play for the NHL club at any given time though, since the NHL roster limit is 23. If a team uses all 50 contract slots, it's enough players to completely stock an NHL and AHL club, and have a few left over to send to the ECHL. Most teams do come close to the 50-contract limit, leaving just a little room for potential trades.
Occasionally someone will say that a team should "release" a contracted player. This isn't something that can be done in hockey, unfortunately, as it can in football. Contracts are guaranteed. Think of it like the law of conservation of energy.* Contracts cannot be destroyed during the year, they can only be bought out during a specified period in the offseason. Contracts "taking on different forms" is how you end up with players like Arturs Irbe playing in the ECHL -- the Hurricanes had no other way to get rid of him.
In addition to the 50 signed players, a team may have 40 more players it owns the rights to, but are currently unsigned, up to 90 total on what's called the "reserve list." (In the last CBA, the reserve list was 75, but this number was raised These players are draft picks, or restricted free agents who are holding out.
To tie this in to current events, there are some teams that still need to get to the salary floor for 2008-09. Signing more and more cheap players isn't going to get them there, because they'll run out of contracts. And they can't just give their current players more money either, since contracts cannot be renegotiated. This means they will have to trade their way up to the floor. With a salary floor of $40.7 million and a 23-man roster limit (minor leaguers don't figure in), a team needs the average salary per player to be at least $1.77 million. With a minimum salary of $475,000, you need a fair number of multi-million dollar salaries to balance it out. Parity of course is the goal, but the logic of the rules has the potential to lead teams into odd moves.
*The law of conservation of energy states that energy may neither be created nor destroyed. Energy in a system may take on various forms (e.g. kinetic, potential, heat, light). Therefore the sum of all the energies in the system is a constant.