Definition of in sync
1 : in a state in which two or more people or things move or happen together at the same time and speed The dancers moved in sync. The film's sound and picture need to be in sync. —often + with She moved in sync with her partner.
2 : in a state in which two or more people or things agree with or match one another and work together properly Our ideas are in sync. —often + with The quarterback was in sync with his receivers.The President is not in sync with the concerns of the people.