The HoloNet, also spelled Holonet, was a galactic communications grid that was developed and used by the Galactic Republic and, later, the Galactic Empire. The HoloNet was a near-instantaneous communications network commissioned by the Galactic Senate to provide a free flow of hologram and other communications among member worlds. It vastly sped up galactic communications, which had previously depended on subspace transmissions or relays.
A message is first broadcast from a planet, in hyperspace, or from another point of origin; from there, it is routed from the point of origins transmitter through millions of hyperwave transceivers buried in hyperspace to a Holonet relay, where it is sorted through the relays computer sorters and decoders, and then routed along appropriate transceivers to its destination. The transceivers themselves transfer the messages across the galaxy through s-threads. This enables data to be sent and received at faster-than-light speeds, ensuring near-instantaneous communication from one end of the galaxy to the other, by relaying the information from origin, to transceiver, to relay, to transceiver yet again, and then to its final destination.
It should also be noted that the information transmitted via the HoloNet was almost impossible to be captured by spies, thanks to s-thread's incredibly narrow dimensions. The only way to do so was to attach a listening device to the sender, the relay station, or the destination itself.
The HoloNet system was an extremely costly expenditure, both for transceiver placement/maintenance (funded by the government) and for consumer HoloNet equipment. However, it was one of the major methods of communication in the galaxy. One of HoloNet's services was the "Imperial.emp", a service that even Darth Vader used. HoloNet was also known for containing several forums, including the one called Naboo message exchange.
Created thanks to the Galactic Senate's efforts many years before the Clone Wars, the HoloNet quickly expanded throughout the galaxy, ending up with at least one emitter/receiver device located on virtually every planet of the Galactic Republic.
In 22 BBY, plans to expand the HoloNet to the Outer Rim Territories were delayed due to budgetary restructuring according to the General Ministry Communications Agency. 250,000 worlds in several sectors, including Portmoak, Arkanis, Parmic, Quence, and Kathol, were not to see access for one fiscal year. Where they lacked in primary HoloNet conduits, they made up for with a network of Subspace relay stations for intersector communications, resulting in delayed galactic news reaching those sectors within days or weeks.
During the Clone Wars, the Confederacy created the CIS Shadowfeed, a network of hyperwave transceivers similar to the Republic's HoloNet News channel. During this time, both sides used the HoloNet to broadcast propaganda.
When Emperor Palpatine assumed power, large portions of the HoloNet were shut down to prevent news of the Empire's atrocities from spreading quickly. During the time of the Empire, the HoloNet was strictly controlled, used mostly for Imperial Military communications. This greatly inhibited the ability of groups like the Alliance to Restore the Republic to communicate, and arguably also had an isolating effect on the many planets over which the Empire held power. During this period, Ebenn Q3 Baobab created an alternative HoloNet since the official HoloNet disseminated only Imperial propaganda without the "complication" of unapproved free speech. After the Empire fell, HoloNet channels were reopened and security was lifted, restoring free speech.