Complex sentence: Quests may be undertaken for their various rewards, or to acquire "fame," which allows a character to become well-known and respected by NPCs; a higher fame rating will open up new interactions and quests with NPCs.
Split into simpler sentences: Quests may be undertaken for their various rewards, or to acquire "fame". Fame is a term used to describe how well-known and respected a player is to NPCs, a higher fame rating will open up new interactions and quests with NPCs.