The term "ROS Package" is used numerous times in REP 149 but not defined in that document. It should probably be defined in a REP or in some sort of authoritative glossary relevant to ROS2.
There is a definition in http://wiki.ros.org/Packages is clearly tailored to ROS1 as it is in terms of ROS_PACKAGE_PATH.
This term is needed to disambiguate from other types of packages (CMake project, Python project, etc.). It's unclear if "ROS Package" is more narrow, less narrow, or equivalent to "Packages recognized by colcon".
Originally raised in #265