The phrase "pudding layer" refers to a thick or heavy layer of something, similar to the thickness of pudding. It is often used to describe the visual appearance or texture of a certain substance. Full definition
Spread remaining 3 cups of whipped topping over pudding layer; swirl melted chocolate throughout whipped topping. (piarecipes.com)
My favorite part was the vanilla pudding layer... this was delicious and I used a tsp of vanilla extract since I couldn't find vanilla bean. (epicurious.com)
Allow pudding to cool enough to eat, or cool completely for a thicker pudding layer. (angelaskitchen.com)