noun
A mathematical term for a mapping between function spaces, such as a differential or integral operator.
線形作用素の理論は関数解析の基礎である。
The theory of linear operators is fundamental to functional analysis.
この微分方程式は、ある作用
This differential equation can be formulated as an eigenvalue problem for an operator.
Compound of 作用 (action, operation) and 素 (element, basis), likely a calque from a Western mathematical term.