All this data is potentially out of date, and should be taken with a truckload of salt
The hull or structure of a ship is the internal framework upon which the ship's armor and modules are placed, and where the ship's powergrid, CPU, and the like are presumably located. Like armor and shielding, it has a numerical rating, and in many other ways is treated by the game as a rating parallel to these, but there are significant differences between these two and the hull.
An attacker must wholly deplete a ship's shields and armor before damage will degrade the target's hull. Should a ship's hull be reduced to zero, it will be destroyed.
A ship's hull is thus technically the third, and rather fragile, level of a ship's defence, after its shields and armor, but there are fundamental differences between the hull and these other, more formal defensive systems that differentiate them. Chief among these differences is that, as mentioned above, if a player's ship's hull is reduced to zero, the ship will explode and dump the player's capsule into space, regardless of whether any shielding or armor remains on the ship (although this last condition is difficult if not impossible to put into practice on a player-controlled ship, it is sometimes seen on NPC targets). A second distinction is that as a ship's hull becomes damaged, installed modules also risk becoming damaged and unable to activate. This damage must be repaired in a repair shop while the ship is docked.
A small variety of modules are able to influence a ship's hull, including:
- damage controls
- hull repair systems
- nanofiber internal structures
- reinforced bulkheads
- remote hull repair systems
Variations on the phrase, "Real men hull tank," are a running joke in EVE-Online, although this is unadvisable in the extreme to actually put into practice.