What does it mean when something says that UNIX device files are static?

I've read up on . In the "overview" area, Wikipedia mentions that "unlike typical Unix systems, where the tool nodes in the/ dev directory site have actually been a fixed set of files, the Linux udev tool supervisor dynamically gives just the nodes for the tools in fact offer on a system".

What does it suggest when it claims "static set of files"? Does it suggest that there are constantly /dev files yet they do not constantly indicate an actual tool?