Solar system

A solar system (more properly, star system or stellar system) is a grouping of one or more stars, commonly orbited by one or more planets and various other cosmic detritus. Transformers typically travel to different star systems in the course of their adventures. As star systems are generally several light years apart, this requires some sort of faster-than-light propulsion, or an instantaneous gateway system of some kind, such as a space bridge.

Fiction
Notable solar systems in Transformers fiction include:
 * The Sol system, dominated by the sun, appears in almost every Transformers story. Its known orbital bodies include:
 * Mercury
 * Venus
 * Earth
 * Mars
 * The asteroid Ceres
 * Jupiter, and its moon Io
 * Saturn, and its moon Titan
 * Pluto

Marvel Comics

 * The Alpha Centauri system, home to the planet Cybertron.
 * An unnamed system where the Matrix Quest took place, home to the following planets:
 * Cheyne
 * Pz-Zazz
 * Pequod
 * Cameron, and its barren moon VsQs

IDW Comics

 * The Lambda Scorpii system, also home to the planet Cybertron.

Those poor, confused writers
A star system should not be confused with a galaxy, which is a massive grouping of millions of star systems. A single galaxy is unfathomably huge, with our own Milky Way Galaxy containing several hundred billion stars. The distances between galaxies are several orders of magnitude greater than the distances between the star systems they contain.

Unfortunately, in Transformers fiction, "galaxy" is frequently used in places where "star system" makes a lot more sense, or at least is not as jarring. Given that all interstellar travel is based on fictional technologies, it's not inconceivable that characters might actually come from or travel to other galaxies. But the notion seems an unnecessary complication at best (a single galaxy is a more than ample playground for fictional adventures), and often outright contradicts information given elsewhere. Cartoon animation, for example, almost never supports the idea that characters actually leave the Milky Way Galaxy.

Notable examples of galaxy/solar system confusion include:
 * "Primal Fear!"
 * "The Ultimate Doom, Part 1"
 * "The Test"