Final answer:
Syncrony means simultaneous action, development, or occurrence of events, significant in the concept of the relativity of simultaneity in physics.
Step-by-step explanation:
The term Syncrony refers to the simultaneous action, development, or occurrence of events. In the context of physics, particularly in the discussion of the relativity of simultaneity, it involves two events being measured as occurring at the same time by an observer. This notion is important in understanding the principles of Einstein's theory of relativity, which shows that simultaneity is not absolute but relative, depending upon the observer's frame of reference.