Catkin is a collection of cmake macros and code to build ROS packages

From the ROS Wiki:

catkin is the official build system of ROS and the successor to the
original ROS build system, rosbuild. catkin combines CMake macros and
Python scripts to provide some functionality on top of CMake's normal
workflow. catkin was designed to be more conventional than rosbuild,
allowing for better distribution of packages, better cross-compiling
support, and better portability. catkin's workflow is very similar to
CMake's but adds support for automatic 'find package' infrastructure
and building multiple, dependent projects at the same time.

The name catkin comes from the tail-shaped flower cluster found on
willow trees -- a reference to Willow Garage where catkin was created.

WWW: https://docs.ros.org/api/catkin/html/