The primary hull, also known as the main section or saucer section, was a major component of the overall hull structure on many starship designs.
The primary hull usually contained some of the most important areas on the ship, such as the bridge, computer core and crew quarters. In some designs in case of a mishap the primary hull could separate from the secondary hull.
The primary hull was often referred to as the saucer section on Starfleet designs as they were circular in shape. The primary hull was usually located above and forward of the secondary hull, sometimes connected via a interconnecting hull.