[Discuss what a class is. This will be, I suspect, a part of the overall object oriented information here on the wiki]
A class, in object orientation parlance, an abstract description of the executable actions and type of data and state that an object instantiation of said class will have.
A class can consist of state representation, data, and executable code such as initialization, cleanup, and operations (frequently called methods) that the object can invoke.
Yuck - don't like that definition!
The string "class" is also used as an extension command name, at least within itcl.