essentially contested concept
ambiguity – Type of uncertainty of meaning where several interpretations are possible
concept creep – Expansion of a concept to the point of meaninglessness
demonstrative – Words indicating which object is being referred to
fact–value distinction – Distinction between what is and what ought to be
floating signifier – Signifier without a definite referent
ideograph (rhetoric) – Type of word in political discourse
indexicality – Sign pointing to or indexing an object in its context
meaning (philosophy) – Philosophical conception of meaning
natural kind – Concept in the philosophy of science
vagueness – Property of predicates in linguistics and philosophy
What Is Art? – 1898 book by Leo Tolstoy
https://en.wikipedia.org/wiki/Essentially_contested_concept