So what's the difference? Well a gateleg table has a 'gate leg' on either side of the centre which is on hinges, swings out from underneath, and supports the leaf. They can be very compact when both leafs are folded down with our smallest only 16" (15cm) wide when closed.
A dropleaf table on the other hand has smaller leafs which are supported by spring loaded hinges which lock in to place. They have a wider centre so aren't as compact as the gatelegs when both leafs are closed.