A concept may be considered vague
In analytic philosophy and linguistics, a concept may be considered vague if its extension is deemed lacking in clarity, if there is uncertainty about which objects belong to the concept or which exhibit characteristics that have this predicate (so-called “borderline cases”), or if the Sorites paradox applies to the concept or predicate. Williamson, T. 1994. Vagueness London: Routledge. The history of the problem of vagueness is traced, from the first Sorites Paradox to contemporary attempts to deal with higher-order vagueness such as many-valued logic, supervaluationism, and fuzzy logic. Technicalities are kept to a minimum to favor a clear account, extremely useful to both students and researchers. In everyday speech, vagueness is an inevitable, often even desired effect of language usage. However, in most specialized texts (e.g., legal documents), vagueness is distracting.