A space bridge is a technology for instant travel between distant points in space. In the Transformers world it solves a simple problem: how to fight on two planets at once when they're vast distances apart.
The classic space bridge
In the 1984 cartoon the Decepticons use a space bridge to send Energon from Earth to Cybertron. It's an arch-shaped portal linking the two planets. Many episodes revolve around the Autobots trying to destroy the bridge or intercept the cargo.
The ground bridge
Transformers: Prime introduces a smaller version — the ground bridge, built by Ratchet. It moves the heroes anywhere on Earth in seconds, but needs exact coordinates and lots of power. That explains how a small team of Autobots can be everywhere at once.
Why it matters for the plot
Bridges make stories faster but also create risks: a broken bridge can cut heroes off from home, and an enemy bridge can deliver an army straight to the base. In Dark of the Moon a network of bridges is part of the plan to bring Cybertron to Earth.
