Netlink is an inter-process communication protocol that can be used for communication between processes, or with the kernel. It is implemented by Linux.
Many protocols exist on top of Netlink. The most famous are used to configure network-related functions in the kernel, such as firewall, route table or IP addresses of interfaces.
This library implements the low-level bits of the code by providing data structures that are close to their C counterpart, and basic procedures to initiate communication.