They are both used to reduce paint. Reactive reducer is a catalized reducer for base coats. It has a shorter pot life and once mixed, it must be sprayed. If you try to save it, it will gel. When a base coat is reduced with a non catalized reducer, you can put the unused portion back into the can and re-use it later.
I should add that a catalized base coat also has better adheasion, and is recomended for custom work, and blending.
Austin