noun
Mathematical term for a quantity that remains unchanged under transformations or operations.
この変換の下で不変量を求めよ。
Find the invariant under this transformation.
エネルギーは物理系の重要な不変量である。
Energy is an important invariant in physical systems.
不変 is an adjective meaning 'unchanging' or 'immutable', whereas 不変量 is the noun for an invariant quantity.
Compound of 不変 (invariable) + 量 (quantity). A technical term likely coined in the context of modern mathematics and physics.