Advanced Ships are an official subclass of ships in Galaxy. They are set apart from regular ships due to their above-average stats, cost, and the fact that they are purchased solely with credits and special parts through specific quests.
For more info about acquiring them, visit Advanced Ship Computers.
In version .75a9, the Slipstream became an Advanced Ship, gaining numerous buffs.
In version .73a3, the Galaxy was put on the build menu as a VIP ship and is no longer an Advanced Ship.
In version .69e, Borealis became an Advanced Ship (and got buffed) and every Advanced Ship was made available for a month (except the Osiris, as the quest for it was disabled). Their prices were increased as well (e.g. Helios and Imperator price increased from 600k credits to 1.5M credits and 1.4M credits respectively).
Part-way through version .66b, Advanced ships were made partially limited -- only one was available via a quest that changed every month (Galaxy was the only exception, as it was still bought at the Advanced Ship Computers). This followed a previous change that increased some ships' prices and removed ore/items from the build costs. They have a unnaturally high cost for their class, in exchange for superior stats.
In version .65b, Artifact Ships were re-enabled, but no longer cost artifacts to create. Instead, their prices rose dramatically and all ships were to be created through special quests. They were also renamed "Advanced Ships" due to the removal of Artifacts from their creation requirements.
Previously, in version .65a (?), all Advanced Ships ("Artifact Ships") were disabled due to the discovery of an Artifact duplication glitch that has yet to be patched.