A respectful, somewhat formal term for one's own father, used especially in samurai or historical contexts. In modern Japanese, it sounds old-fashioned or literary; お父さん is the usual everyday term.
Father is in his study now.
In period dramas, there are often scenes where a samurai's child calls their father 'chichiue'.
父 is the plain humble term for one's own father, while 父上 is an old-fashioned, respectful term historically used to address or refer to a father with honor.
Compound of 父 (chichi, 'father') and 上 (ue, 'above'), an honorific suffix. The exact historical derivation is uncertain, but it follows a pattern of respectful address using 上.