Class

• A teaching group of pupils, in a school or other place of learning.
  

• A mathematical object, like a Set, but wider.  (i.e. all sets are Classes, but not all Classes are sets. As a corollary, any class under the first definition is also a class under the second definition.)
  

• An adjective or interjection indicating something is Cool.  In rather cool fashion, there is also a Russian adjective or interjection, pronounced almost exactly the same, with fairly similar meaning.