In the Transformers universe, "gestalt" is the unofficial generic term for a team of robots who combine together to form a larger robot. (They're also called "combiners" by the uninitiated.) The idea was borrowed from Voltron, but probably goes back much farther than that.
The first gestalt team was the Constructicons in 1985, and their success led to the rapid introduction of several teams in the next three years. These included the Aerialbots, the Protectobots, and the Technobots on the Autobot side, and the Stunticons, the Combaticons, the Terrorcons, the Predacons, the Seacons, and the Monster Pretenders on the Decepticon side.
These gestalt teams were all built on what was called the "Scramble City" model, after the Japanese toy line from which they were taken. Not only could any smaller gestalt team member become any arm or leg (something not possible with the Constructicon team), but they could be interchanged with arms and legs from other gestalts as well.