The phrase "prepared ramekins" refers to small cooking dishes that have been greased or lined with ingredients in advance, ready for the next step in the recipe. Full definition
Spoon chocolate mixture into prepared ramekins. (myrecipes.com)
Divide batter among prepared ramekins, filling completely. (epicurious.com)
Heed Katzie's advice and prepare your ramekins properly: brush them with softened butter (not melted), using a pastry brush to coat the sides with upward strokes. (epicurious.com)