Casual Meals, depending on ship, consists of Steamers, Planks, Alfredo's, etc. These use to be free but have been added to the packages.
Specialty restaurants, once again depending on the ship, consists of Crown Grill, Sabatinis and were extra ($35/pp currently). If you purchase the premium package you get 2 (I believe) free.
Heres a good article for reference https://www.cruisewith.co.uk/cruise-tips/princess-cruises-dining