The Xenomorph Empress is a step above the Xenomorph Queen in the Xenomorph hierarchy, but a step below the Queen Mother.
InformationAn Empress is an older and stronger Xenomorph Queen. Though she serves virtually the same purpose, she also generally rules over one or more Queens as a sort of "Queen of Queens" or High Queen. As they do not commonly feature in the Aliens or Alien versus Predator franchise, little is known about them.
How Empresses emerged in a hive was started from competitions between presenting multiple Queens in a Hive. Should one of the Queens able to best another, the victorious Queen would become Empress.
Empress Xenomorphs' physiology has been seen to differ, with some appearing similar to typical Queens (albeit considerably larger), while others have been seen to have unique traits. These include significantly tougher exoskeletal armor compared to other Xenomorphs. Empresses have been seen to possess an ability to summon lesser castes of Xenomorph to their aid, similar to Praetorians, as well as driving all adult aliens around them into a combat frenzy, causing them to be more dangerous than usual.