What is the difference between a PC optimizer and a PC cleaner?

This varies per program. Some Optimizers offer similar tools to cleaners. However usually optimizers will remove temp files, defrag drives, and keep system files “optmized” and a cleaner will search the PC for rogue files, trojans, and spyware.

But it all depends on the application you are looking at. If you are trying to compare similar programs I can possibly offer more information about them.