Art-Net is an Ethernet based control protocol that was invented by a company called "Artistic Licence" and released for royalty free usage.
The basics of Art-Net are that over a standard IP based private LAN network (AKA same way you get internet but not actually connected to the internet, hopefully...) you can have one or multiple controllers sending one or multiple "DMX Universes" of data to any number of receivers. Each "Universe" is the same as a "Universe" of regular DMX in that it is 512 "channels" each with a value of between 0 and 255. These packets are usually sent between 30 and 45 times every second.
Art-Net can theoretically send up to 32,768 universes over one network connection, though other limitations prevent this from being practically possible.
Similarly, there is also Streaming ACN, another protocol that can send multiple DMX universes over a network connection.