The word synoptic as used in science means covering everything, i.e., "the whole picture". The word is related to synopsis, which means roughly the same as abstract or summary, i.e., a description of an entire written work.
Meteorology uses the term synoptic, and astronomy has as well. In meteorology, it means "involving all the Earth", or at least far beyond a single locality, e.g., using data from many locations and modeling the weather over a large region.
In astronomy, it has been used to indicate "including the whole sky", i.e., celestial sphere, or much of it. Perhaps it has also been used in other senses.