1. To happen, function, or move at the same time and pace as someone or something; to be simultaneous. Every soldier in the squad was perfectly in sync while marching. Is it just me, or is the audio not in sync with the movie?

2. To share the same or similar goals, ideals, desires, likes, dislikes, etc. with someone; to have the same or similar perspectives or opinions as someone. Throughout the date, it just seemed like she and I were totally in sync about everything we brought up. If your team isn't in sync with one another, you're going to have a hard time getting this project done.