What does "synoptic" mean in avionics?
Synoptic refers to the active system diagrams that are selectable, usually on one of the middle displays above the center console.  If you want to know what the hydraulic system  is up to, you can select the Hydraulic Synoptic and an active diagram of the hydraulic system appears, showing what's pressurized and what's not, valves open and closed, the pressure values, quantities, etc.  There will be one for most of the major systems, hyper simplified compared to a normal system schematic because only the essential information is presented.