The Synod is a group of mages hailing from Cyrodiil. Formed sometime after the disbandment of the Mages Guilds across Tamriel following the Great War, they scour Tamriel for magical artefacts of great power for 'safekeeping'.
In Skyrim, the Synod was busy trying to activate the Oculory in Mzulft, believed to be a magical telescope that would reveal the location of powerful magical artefacts across Skyrim. The expedition was stalled when the Focusing Crystal they were using was damaged and a new one had to be shipped in from Cyrodiil.
In the time between the experiment stalling and the Dragonborn arriving at Mzulft, the Falmer that were driven out of the main chambers returned with a vengeance and killed all but one member of the expedition.
The Dragonborn succeeded in reaching the survivor and activating the Oculory only for the survivor to find out that there was some massive magical interference, from the Eye and Staff of Magnus, preventing the Oculory from providing accurate readings.