 One of the distinctive features of Russell’s definition is that it treats the expression “the x such that Fx” as an “incomplete symbol.” Such symbols have no meaning in isolation but are given meaning by contextual definitions that treat of the sentential contexts in which they occur (cf. PM, 66). Incomplete symbols do, of course, have meaning because they make a contribution to the meanings of the sentences in which they occur (cf. Principles, Introduction, x). What is special about them is that they make this contribution without expressing a propositional constituent. (For more on the nature of incomplete symbols, see Pickel 2013)