Maybe my previous post here 
<https://groups.google.com/d/msg/voidlinux/WVcjzZ7eEME/z4DACiUKcZwJ> can 
shed some light :)

Here is a ficticious example: A package may need tools like "cmake" and 
"pkg-config" to run through its build-process and the "qt" library is 
needed to build and execute it. These would be the different dependencies:

*hostmakedepends:* cmake, pkg-config
Installed and executed on the host in its architecture to run through the 
build process

*makedepends:* qt-devel
For compiling purposes the -devel variant of a library is needed. These 
dependencies are automatically installed seperately for each target 
architecture

*depends:* qt
Needed to run the program on the target system. This is automatically 
detected in many cases so you probably will not need to specify it at all.