X font server (xfs)
A separate service that handed out fonts to X servers over the network, from an era when fonts were something the server owned.
In the core protocol the X server fetches fonts on the client's behalf, so every display needed its own font files. X11R5 in 1991 introduced the font server: a daemon, usually on TCP port 7100, that X servers could add to their font path with xset fp+ tcp/host:7100. A whole department of X terminals could share one collection, and the font server could rasterise scalable formats for them.
Late-1990s Linux distributions ran xfs locally, mainly to bolt on TrueType support. It worked, slowly, and a hung xfs could freeze the entire desktop. Once Xft and fontconfig moved fonts to the client the need evaporated, and distributions dropped xfs in the late 2000s.