Full Idea
For Frege, a predicate does not refer to the objects of which it is true, but to the function that maps these objects onto the True and False; ..a predicate is a name for this function.
Gist of Idea
For Frege, predicates are names of functions that map objects onto the True and False
Source
report of Gottlob Frege (works [1890]) by Colin McGinn - Logical Properties Ch.3
Book Reference
McGinn,Colin: 'Logical Properties' [OUP 2003], p.67
A Reaction
McGinn says this is close to the intuitive sense of a property. Perhaps 'predicates are what make objects the things they are?'