Quasi-quotation

Quasi-quotation is a linguistic device that facilitates rigorous and terse formulation of general rules about linguistic expressions while properly observing the use–mention distinction. It was introduced by the philosopher and logician Willard van Orman Quine in his book Mathematical Logic, originally published in 1940. Put simply, quasi-quotation enables one to introduce variables that stand for a linguistic expression in a given instance and are used as that linguistic expression in a different instance.

For example, one can use quasi-quotation to illustrate an instance of substitutional quantification, like the following:

"Snow is white" is true if and only if snow is white.
Therefore, there is some sequence of symbols that makes the following sentence true when every instance of φ is replaced by that sequence of symbols: "φ" is true if and only if φ.

Quasi-quotation is used to indicate (usually in more complex formulas) that the φ and "φ" in this sentence are related things, that one is the iteration of the other in a metalanguage.

Read more about Quasi-quotation:  How It Works, A Caution