Server
A computer that waits for and answers requests from other computers.
Technically "server" isn't hardware but a role. Your laptop can be a server for 30 seconds if you run python -m http.server. But in practice, people mean a computer in a data centre, always on, with serious connectivity.
Forms: VPS (shared machine, cheap, from ~SEK 50/mo), dedicated (whole machine, more expensive), cloud instance (created and torn down on demand), shared hosting (you share a server with 100 other sites — cheapest but least flexible).