hematicians use the word in a very particular way, which 
&gt;in its full form is written "proper class", to refer to things that 
&gt;anyone but a mathematican (and even some of them) would call a set, 
&gt;except they are so big that if they are accepted into the 
&gt;set-theoretic universe they would give rise to paradoxes.

This use is known only to the subgroup of mathematicians who
are working on logic and foundations.  Working mathematicians
in algebra, topology, differential equations, etc., may be
