Gradability is a grammar teacher’s word for this fact: some describing words can show more or less of a quality. If an adjective has gradability, you can say very quiet, quite quiet, quieter, the quietest. If it does not, careful English treats the quality as all-or-nothing: dead, pregnant, square. You meet the noun in language classrooms and linguistics, not in the street — nobody at the market says “I love the gradability of this word.” Though actually, real speech is messier than the tidy classroom split. People say very unique all the time, and some adjectives sit in the middle, so gradability is the usual pattern, not a police rule. The idea is still useful: it explains why very tall sounds natural and very married sounds like a joke.

（語法）可分級性