Why is apple called a false fruit? Which part of flower form its fruit?

Explanation

When only the ovary of the flower grows into the fruit, it is commonly known as true fruit, e.g. pea.
When other floral parts such as the thalamus/receptacle or calyx, may also grow and form fruit. Fruit is called falsel spurious or Pseudocarp.e.g. Apple-the fruit develops from the Thalamus.