Each player has a limit as to how many objects that player may create, called their 'quota'. Every object they create lowers the quota by one and every object they recycle increases it by one. If the quota goes to zero, then that player may not create any more objects (unless, of course, they recycle some first).
The @quota command prints out your current quota.
The quota mechanism is intended to solve a long-standing problem in many MUDs: database bloat. The problem is that a large number of people build a large number of dull objects and areas that are subsequently never used or visited. The database becomes quite large and difficult to manage without getting substantially more interesting. With the quota system, we can make it possible for players to experiment and learn while simultaneously keeping random building to acceptable levels.
To get a larger quota, talk to a wizard. They will take a look at what you've done with the objects you've built so far and make a determination about whether or not it would be a net gain for the MOO community if you were to build some more things. If so, they will increase your quota; if not, they will try to explain some ways in which you could build things that were more useful, entertaining, or otherwise interesting to other players. Wizards may be more impressed by objects which are interactive and employ a fair number of verbs.