Netcat is a simple Unix utility that reads and writes data across
network connections using TCP or UDP protocols. It is designed to be a
reliable back-end tool that can be used directly or easily driven by
other programs and scripts. At the same time, it is a feature-rich
network debugging and exploration tool, because it can create almost
any kind of connection you may need and has several interesting
built-in capabilities.

Find the documentation in /usr/share/doc/packages/netcat/README.