Basics

A Data Storage Server for a LAN (Although if not Air Gapped can be accessed remotely)
Often abbreviated as NAS
Useful for a Personal (ie no Monthly Fees short of Cost of Electricity and paying off components) version of Cloud Storage
Offloads Storage Needs from Smartphones, Laptops, etc while still "keeping" the data
For Group Environments it can allow for high speed data tranfer across the editing team since it is all on a local server, and you can even use high speed networking such as 10 Gigabit Ethernet , as opposed to having to upload/download to a nearby cloud server as fast as your IP allows, and for each pc

Internal Links

RAID Array (A method of redundant multi-disc storage often used in NAS devices, which can also be used as a standalone External Drive in theory via USB-C or Thunderbolt 3 etc)