These are sockets which are reachable from the Internet directly. The link
program tlink is the provided facility for such communication with MiniVend; you may also
use your browser to talk to the socket directly if you have it mapped to a
catalog with the global TcpMap directive.
To improve security, MiniVend usually checks that the request comes from one of a limited number of systems, defined in the global TcpHost directive. (This check is not made for the internal HTTP server.)