ˌɒpəˈɹeɪʃən ˌɑpəˈɹeɪʃən pəɹ.ˈfɔɹ.məns performing or able to perform its regular function a functioning flashlight process or manner of functioning or operating the power of its engine determines its operation the plane's operation in high winds they compared the cooking performance of each oven the jet's performance conformed to high standards