The nexus is a mammoth, pyramidal structure that looms over each and every protoss settlement. It serves as a psychic anchor, allowing the protoss to access the psionic matrix from even across the galaxy. The nexus also manufactures probes and has a processing center for minerals and vespene gas.
Khaydarin crystals are located within each nexus. They can be used as a defensive measure when the psionic matrix is supercharged by a mothership core. In turn, each nexus is linked to these cores through its khaydarin crystals, and can serve as a warp beacon to initiate recall. A nexus can also produce a burst of energy that creates a chronal distortion field, briefly accelerating the production of a single structure.
The nexus serves as the hub of any protoss base. Unlike most other protoss buildings it can be warped in without a pylon. It constructs probes and serves as a processing center for minerals and vespene gas.
In Heart of the Swarm, the mothership core uses this ability on a nexus, which gains a photon cannon-like weapon. The weapon has range 13, targets air and ground and deals 20 damage. The weapon lasts 60 seconds and has its own cooldown of 1.25.
In Legacy of the Void, this ability is cast on pylons, dealing 30 damage with a cooldown of .71 seconds.
The following section contains information from a previous version of StarCraft II which is no longer valid.
The nexus went through many small changes. As a primary structure, the scale was adjusted often, specifically the pyramid shape in the middle. The only significant overhaul was done with the intention of increasing the polycount on the curved surfaces around the structure.
The nexus will undergo a redesign in an upcoming patch to account for the removal of the mothership core. Its chrono boost ability will be redesigned, it will gain the mass recall ability, and gain a shield boost ability. It will start with 50 energy as opposed to the current 0.
A "nexus" is a term that refers to "a central or focal point," or "a connection or series of connections linking two or more things." This fits the nexus given its central role in the protoss tech tree.
The Nexus is the name of the primary setting of Heroes of the Storm. Its shared name with the protoss nexus is brought up by Jim Raynor in the game's original tutorial, though this has since been removed.