This refers to the property of adjectives (and some adverbs) to express degrees of application of some notion. For example, the property of being warm can be graded, because we can have warmer and warmest (these are comparative and superlative forms, respectively) and also very warm, where the adjective is preceded by an intensifier.
A very simple definition of adjectives that has sometimes been used is that they are ‘descriptive’ words. But this isn’t really very helpful. Lots of word classes can be ‘descriptive’: a noun like funeral is fairly descriptive, as is the verb leap. We might also say that the adverb quickly describes the verb ran in a sentence like He quickly ran.
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