A Nexus is a magical teleportation device. A Nexus is constructed of eight obelisks covered in runes, tied into a massive magical construct resembling a wheel with eight spokes. The entire complex is the size of a small city.
A Nexus is normally only capable of teleporting people from one Nexus to another, but if modified or tied in with a person's innate Motion Magic, it can be used to teleport people anywhere. It's also possible to use a Nexus as a focus for someone's innate Time Magic in order to allow them to target time travel more precisely.
Someone can link themselves into a Nexus in order to bind themselves to a beacon that they can use to Recall to. With greater skill, one is even capable of linking their Motion Magic to a Nexus to piggyback across it, using the Nexus to give a boost to their own teleportation without fully materializing in the Nexus itself. This is the principle behind the nexal drive developed by Suzcecoz.
The artificial plane of Vel'kira consisted of a large number of cities, each of which had a Nexus for travel between them. When Vel'kira collapsed, many of those Nexi remained intact in the fragments.