When you and your friend, family member, etc doing something at the exact same time such as saying the same thing, dressing in the same outfit, or calling each other at the same exact time.
Who knew Caitlin and Siobhan would where the exact same hoodie, jeans, AND necklace on the same day! They must be physco-synced.
As we sat at the movie, both Caitlin and Siobhan yelled "Thats so awesome!" Sometimes I wonder if its more than just physco-syncronicity...