Communication satellites, also known as comsats, were a form of high-bandwidth relays that were used for communication between two points that were at a large distance.
During the Trade Federation's invasion of Naboo, they used slave satellites to amplify the signal from Droid Control Ships.
During the Galactic Civil War, Ansible Incorporated manufactured several different models of communication satellite that came into widespread use throughout the galaxy.
The Galactic Empire maintained a vast network of communications satellites used for surveillance with each satellite linked to the Imperial Security Bureau in Imperial City. The network allowed Imperial Security to monitor and control the Core Worlds and other territories of the Empire. At its peak, the network spanned as far as the Outer Rim Territories. Satellites were often hidden in asteroid fields or by uninhabited planets and were usually protected by mines. Destruction of surveillance satellites was actively pursued by the Rebel Alliance as a means to disrupt Imperial control.
The Rebels used some communications satellites, stolen from Orron III, to help them intercept Imperial transmissions while attempting to learn more about the Death Star I.