Full Idea
A principle of abstraction is 'conceptual' when the items upon which it abstracts are concepts (e.g. a one-one correspondence associated with a number), and 'objectual' if they are objects (parallel lines associated with a direction).
Gist of Idea
We can abstract from concepts (e.g. to number) and from objects (e.g. to direction)
Source
Kit Fine (The Limits of Abstraction [2002], I)
Book Reference
Fine,Kit: 'The Limits of Abstraction' [OUP 2008], p.1