indeclinable; particle
Linguistics term for words that do not inflect, such as particles, adverbs, conjunctions, and interjections in Japanese grammar.
Japanese indeclinables include particles, adverbs, and the like.
活用語 refers to inflecting words (verbs, adjectives, etc.), the opposite of 不変化詞.
Compound of 不変 (invariable) + 化 (change) + 詞 (word), literally 'invariable word'. A calque from Western linguistic terminology.