A common word for 'father.' While 'otousan' is more familiar in speech, '父親' is used in formal contexts and general descriptions.
彼の父親は医者で、町で有名だ。
His father is a doctor and is well known in the town.
父親としての責任を強く感じている。
He strongly feels his responsibilities as a father.
学校から父親宛に通知が来た。
A notice addressed to the father came from the school.