Pro tem
Definition 1 of 1
Pro Tip 1/3Temporary Replacement
Used to describe someone taking over a role while the usual person is absent. 
During the director's medical leave, the assistant will serve pro tem.
Pro Tip 2/3Formal Contexts
'Pro tem' is often used in official or formal settings, especially in organizations. 
The vice-chair served as chair pro tem during the meeting.
Pro Tip 3/3Not Permanent
It implies that the position or role is not expected to become permanent. 
She was appointed manager pro tem until a permanent replacement could be found.