Properties -> C/C++ General -> Export Settings
From the documentation...
The export settings page gives you fine grained control of which paths, preprocessor symbols, and library files are exported by a given project's configuration.
When another project's configuration, in the workspace, references a configuration with exported settings, those settings are automatically propagated into the dependent project configuration. CDT also ensures that referenced projects are built as a prerequisite for building dependent projects.
This functionality prevents you from needing to maintain and update the build settings manually between all the dependent projects in your workspace. Simply configure the exported settings, setup the references, and the settings are propagated and kept in sync for you.
What does the term "settings" mean/include?
From the documentation...
You can modify the list of exported elements (include paths, symbols, libraries, library paths)
What does the term "exported elements" mean and what does it mean to export these?