As Danny noted, the lockout is lifted as of right now. Welcome to a brave new world? Not quite, for several reasons...

Judge Nelson's ruling is available here and elsewhere. It is a meaty, 87-page read, with a lot of references to other rulings and historical context that are apt to give you a headache. That said, her arguments appear to be fairly straightforward. Before one reads on to interpret, note that I am not a lawyer and more familiar with European labor law than its US counterpart, but it seems to hinge on the same principles.

First off, the NFL argued that either the court should defer to the National Labor Relations Board rather than make a ruling, and argued that an earlier ruling (Norris-Laguardia) legally prevented injunctive relief. Injunctive relief here means the court immediately lifting the lockout. Judge Nelson dismissed both arguments, the NLRB having no primacy of jurisdiction and waiting on its advise would constitute an unwarrantable delay, while Norris-Laguardia is set up to protect against lockouts from her perspective.

Once jurisdiction is established, there are a number of points that have to be proved before the court can move for injunctive relief. These are always the same, whether it is to bar someone from making or releasing a product when its legal status is unclear (which I'm familiar with), or in a case like this. Judge Nelson pointed to several things in favor of the plaintiff (Brady et al):

• Upholding the lockout would cause irreparable harm to the players, barring their capability to properly perform their jobs and causing financial harm. Lifting the lockout causes irreparable harm to the league (harming its standing in negotiations), but the judge ruled this does not outweigh the harm to the players.
• In the judge's opinion, the arguments brought forth by the players on this case are more convincing than the league's arguments, to such an extent that it is likely that the players are going to win this case, even in appeals. This is known as granting an injunction based on the merits of arguments. The details of these arguments are rooted in the legalese and earlier cases noted above, which I'll just leave be.
• And finally, and this is an argument I'm less familiar with and consider kind of surprising, the judge argues that the public interests tends more towards the players than the owners. I do not know the legal details of this argument, but it seems common sense.

And it is as clear as that. Based on the ruling, the lockout is lifted, and because of the arguments listed above, this ruling takes place as an immediate injunction. When people say there is no "stay", this is what they mean. A stay is a delay of the ruling to allow appeals to take place. If a court can see no harm being caused by a stay, or thinks the plaintiff's arguments hold dubious merit, a stay would have been granted.

But what does this mean for teams...?

That is a much more difficult question. First off, it might not mean anything. As a lawyer representing the players points out here, any court ruling comes with a certain amount of "common sense" leeway. One can not argue the NFL is in contempt because it does not kick off a new labor year immediately, that is a bureaucratic impossibility. For the reason, a de facto "stay" is applied, but it is temporary. How long? That I can't say, but the lawyer gives it "a day or so", which sounds reasonable.

It could also negate all meaning of this ruling. The NFL has already appealed at the US Court of Appeals for the Eight Circuit (and directly to Judge Nelson, according to Peter King). The NFL has requested an "expedited appeal", which makes sense. They need a ruling on the stay before the temporary leeway runs out, because if they kick of the league year in a few days only to be granted a stay a week from now, this would constitute additional harm. The 8th circuit judges have been primarily appointed during the Conservative party's presidential periods, and by comments from journalists have a reputation to be more conservative than judge Nelson was. The court can only grant a stay or not grant a stay, in which case granting a stay is the more conservative option. For this reason, everyone is expecting this to blow over by tomorrow. But it's not guaranteed to. As Sander from Bucs Nation pointed out to me while we were discussing this, it might be possible for the 8th circuit to grant a "partial stay", upholding an end to players being barred from facilities while granting a stay in free agency. I do not know if this is legally possible.

EDIT: the NFL has petitioned Judge Nelson for clarification and a temporary stay while they launch in the 8th circuit appeals process. The league will argue this is necessary not to be thrown into organizational chaos, which would cause irreparable harm. Judge Nelson's ruling seems very firmly worded, so one would assume she's not inclined to give even a temporary stay, but it's possible she'll grant a stay of a number of days. This is the ruling we should be waiting for today.

To grant a stay, the 8th circuit would have to be convinced that any of the arguments listed above are invalid. In others words, they would have to argue that either the harm to the NFL would outweigh the harm to the players, an argument that would likely involve the possible ensuing free agency chaos if no stay is granted, or argue that that the players' arguments do not hold sufficient merit, or more likely a combination of both. I simply have no idea of the likelihood of said arguments. I've seen reports on it being likely or unlikely, based either on the court's conservative nature for the former or on the language of this ruling for the latter. We shall have to wait and see.

That said, the NFL has already stated it has not kicked off a new league year, and it is unlikely to do so voluntarily as it would harm their appeal. That means free agency has not kicked off as of right now. It also means the NFL has the right to still bar players, arguing organisational reasons, at least until tomorrow.

On the other hand, with no lockout in place and no league year yet kicked off, there is one advantage possible in this grey zone: coaches are no longer barred from contacting players. Whether or not coaches will jump on this opportunity is hard to say. They're kind of the forgotten third party, as no matter who wins, owners or players, the coaches can only be harmed by the lockout.

EDIT: as purplepansy pointed out, coaches are already jumping into the limbo and contacting players. This should benefit teams that need updates on players dealing with health or personal issues, as well as allow them to spread updated playbooks to all players under contract for the coming year. In my opinion, this is a smart move for coaches, and I hope our coaches make full use of the opportunity and quickly send out playbooks and communications, as the timeframe in which they can do that might be very short: if a stay is granted, communication will again be barred.

Now to engage in a little bit of what if. What if the stay is not granted tomorrow (or within whatever temporary leeway period is given to the NFL)? Then legally the league is obliged to start a new league year. Legally, it can then no longer bar players from team facilities. Free agency is a more difficult field to resolve. Free agency would exist by definition, but by what rules? It is possible the NFL would be allowed to instate temporary rules of its own crafting. However, more than likely it would be forced to apply 2010 rules for the new 2011 season. What would happen to franchise tags is completely unclear to me, and would possibly be a bone of contention.

Note that while the NFL would be forced to open its facility doors, teams can not technically be forced to sign free agents or trade picks for players. More likely than not, owners would look to prevent said actions from taking place as they would harm their courtroom arguments. But by doing so for any extended period of time, they would risk charges of collusion and significant fines.

Too long, didn't read version: Judge Nelson's ruling will not have any real impact if the 8th circuit grants a stay. If it does not, we enter a period where more likely than not the league year starts under 2010 rules. In that case, I would speculate we're looking at a real possibility of a 2011 year played under 2010 rules.