Within set theory, many collections of sets turn out to be proper classes.

One refers to collections that are not sets as proper classes.

For example, the class of all sets would be a proper class.

In other words, is defined unless a is a proper class.

If you're so desperate to marry again please wait until a lady of the proper class comes along.

A synonym for collections that are not sets is proper class.

Is she your "page three girl" for the proper class?

This led to the idea of a proper class.

Of course, if they do accept me, eventually, I'll be able to go to the proper classes.

And I don't see the pretty young ladies of the proper class rushing off to university to fill the void!