Full Idea
In the unramified theory of types, all objects are classified into a hierarchy of types. The lowest level has individual objects that are not sets. Next come sets whose elements are individuals, then sets of sets, etc. Variables are confined to types.
Clarification
'Ramified' means having complex extensions
Gist of Idea
In the unramified theory of types, the types are objects, then sets of objects, sets of sets etc.
Source
A.George / D.J.Velleman (Philosophies of Mathematics [2002], Ch.3)
Book Reference
George,A/Velleman D.J.: 'Philosophies of Mathematics' [Blackwell 2002], p.46
A Reaction
The objects are Type 0, the basic sets Type 1, etc.