An officer-elect is a person who has been elected to a position but has not yet been installed.[1][2] Notably, a president who has been elected but not yet installed would be referred to as a president-elect (e.g. president-elect of the United States).
Analogously, the term -designate (e.g. prime minister-designate) is used for the same purpose, especially when someone is appointed rather than elected (e.g., justice-designate).