The Imex is an important piece of advanced alien technology, hidden by Lawrence Gordon inside an old Timex watch.
Lawrence's son, Flash Gordon, is originally drawn into adventures in outer space when people from the planet Mongo send Probes through a Rift to Earth, to retrieve the Imex. Flash is imprisoned and questioned by Rankol, but he has no idea what the aliens are talking about, only realizing later that they are referring to his father's watch.
Flash briefly opens the back of the watch, and is shocked to see glowing blue holograms emerge, filling the room with mysterious alien data. To keep it safe, he pretends to destroy the watch. ("Episode 101: Pilot")
The data held inside the watch is important for the development of Mongo's rift technology. When errant rifts open between Mongo and Earth, Rankol explains that it's difficult to calculate the field parameters without the Imex. ("Episode 103: Infestation")