The term frame describes the "ribs" of a vessel or main lateral bulkheads within a ship.
In the Colonial Fleet, frames refer to the ribs that form structural segments of a battlestar. These major structural bulkheads provide structural strength as well as serve as dividers within the vessel's interior space into airtight compartments. Frames form a damage control against hull breaches that could vent atmosphere, equipment or crew into space. Frames help contain decompression within small compartments or bays.
Often when discussing areas of the ship, frame numbers are used to quickly define sections of a vessel. When Galactica is hit with a nuclear warhead in its first encounter with Cylons during the Fall of the Twelve Colonies, Galactica's XO Saul Tigh informs Commander Adama of the extent of the fires burning within the severely damaged port flight pod by referencing what compartments were on fire by saying "everything forward of frame 250". Tigh is referring to the lateral bulkhead within the port side flight pod, number 250, or in other words the 250th lateral structural bulkhead support rib within the hull's superstructure (TRS: "Miniseries").