gears...what does this mean?

[Kalidurga]

As far as shifting under load, one thing you can do is get a 'low-normal' RD. This will make the moving to easier gears (bigger cogs) easier, but it will change your right STI (controls the rear) to a configuration opposite of a road or top normal mtn derailleur.

Can you clarify what you mean by "it will change your right STI (controls the rear) to a configuration opposite of a road or top normal mtn derailleur"? "Low normal" and "top normal" are terms I don't think I've heard before.

Thanks