You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit 19fcf8a045041bcfa69b89310cadcd02c3b804e1)
listen SOCKET,QUEUESIZE

Does the same thing that the listen(2) system call does. Returns true if it succeeded, false otherwise. See the example in "Sockets: Client/Server Communication" in perlipc.