Full Idea
The simple theory of types distinguishes sets into different 'levels', but this is quite different from the distinction into 'orders' which is imposed by the ramified theory.
Gist of Idea
Simple type theory has 'levels', but ramified type theory has 'orders'
Source
David Bostock (Philosophy of Mathematics [2009], 8.1)
Book Reference
Bostock,David: 'Philosophy of Mathematics: An Introduction' [Wiley-Blackwell 2009], p.231
A Reaction
The ramified theory has both levels and orders (p.235). Russell's terminology is, apparently, inconsistent.