DMX stands for "Digital Multiplex" and is a communication protocol that has been used in the professional stage / entertainment lighting industry for over 20 years.
The jist of it is that a "controller" will repeatedly send a list of 512 "channels" (of which each channel can have a "level" of anywhere between 0 and 255).
Each list of 512 "channels" is called a universe. Normal / Traditional / "analog" (a misnomer) / Serial DMX is sent over a 3 or 5 pin XLR cable and is actually an RS-485 serial connection.
The standard defines data being sent over a differential pair of wires on pins one and two of a five pin XLR connector, though many manufacturers use 3 pin XLR or "RJ45" (actually 8P8C) connectors since they are cheaper and easier to come by cables for.
In addition to typical RS-485 based DMX, there are also protocols that send control data via a standard TCP/IP UDP network. The two most common protocols are called "Art-Net" and "Streaming ACN" (or "sACN" for short).
Art-Net theoretically can send up to 32,768 DMX universes via one ethernet cable and sACN theoretically can send up to 63,999 DMX universes. Neither of those numbers are practically achievable, and (especially Art-Net) is much more limited in certain network situations, such as over a WiFi connection.