Metapackages are specialized packages in ROS that only contain one file, that is, a package.xml file. They don't contain folders and files like a normal package.
Metapackages simply group a set of multiple packages as a single logical package. In the package.xml file, the metapackage contains an export tag, as shown here:
<export>
<metapackage/>
</export>
Also, in metapackages, there are no <buildtool_depend> dependencies for catkin; there are only <run_depend> dependencies, which are the packages grouped in the metapackage.
The ROS navigation stack is a good example of metapackages. If ROS and its navigation package are installed, we can try the following command, by switching to the navigation metapackage folder:
$ roscd ...
