worker_connections is the number of simultaneous connections; so they are simply stating how to calculate, for example:
you are only running 1 process with 512 connections, you will only be able to serve 512 clients.
If 2 processes with 512 connections each, you will be able to handle 2x512=1024 clients.
The number of connections is limited by the maximum number of open files (RLIMIT_NOFILE) on your system
nginx
has a better, updated description of worker connections.
fyi, the wiki section is considered obsolete (dont ask), now only the main nginx.org/en/docs are preferred...