In this article we discuss the problems of asking for a definition of quality in education from a philosophy of language perspective. We take the concept of quality as it appears in higher education discourse as our example. More specifically we discuss the possibility of obtaining a precise, unified definition of quality by addressing the problem of asking "what is" questions. We use definition theory and theory pertaining to linguistic vagueness, including Wittgenstein and the idea of family resemblance. We suggest that quality is an inherently vague concept, which runs us into boundary problems and forces us to operate in grey zones. This means that if your "what is" question is a question for the essence of quality, you make demands that the concept cannot fulfil. Recognition of this fact implies that our expectations concerning concept precision and unity should be modified. Our discussion illuminates why it is so difficult to find a definition of the concept of quality.