The same Houdini Engine license can run one of two different types of products:

1. The non-graphical version of Houdini, controlled by a script. This is either hython, which uses the Python language, or hbatch, which uses the hscript language. These non-graphical instances are typically used from batch processes on a simulation or render farm.
2. The Engine plug-ins. These are plug-ins to Unreal Engine, Unity, Maya, etc which allow you to load and cook digital assets inside these other host programs.