A server is a computer that’s configured to efficiently take network requests, process them, and send network responses. You can use any general purpose computer as a server, but custom built computers will likely be more efficient.

Servers can be self-hosted, co-located by high speed internet connections, or part of server “farms” where a lot of computers and hard drives are stored in dedicated racks where a physical hard drive failure means they pull out that drive and pop in a new one, with no loss of data because the data is written to multiple disks.

FWIW, they can definitely fill up. If you can afford it definitely donate and the team will use it to run the platform and pay the devs!