...

<dir_name>_DEPEND_DIRS I'm not sure what this is.  This might define the order in which directories are entered by make.

configure directory

CONFIG_SITE

Your configure directory can have a CONFIG_SITE makefile.  In it we define information about packages that are linked with the application.

...

<package_name>_INCLUDE defines where the library's header files (.h) exist.  This is probably behind an architecture directory, but I don't know why as header files should be consistent across architectures.  Maybe when we build the packages, we copy header files to the architecture directory just for completeness.

RELEASE

In the RELEASE makefile we define the module dependencies for our application.

<module>_VERSION is not required but we use it to make changing module versions easier.  It defines the directory behind the $EPICS_MODULES/<module> directory.

<module> defines the include (.h) and library (.a and .so) search directories.  "include" and "lib/<arch>" are appended to what this macro is defined to be.  Yes, this is confusing.

Application

src Directory

...