Gamopetalous is the term that denotes fused petals in a flower. If the petals are free, then, it is called polypetalous.
Similarly, flowers with fused sepals are called gamosepalous while flowers with free sepals are called polysepalous.
Perianth is the collective term for non-reproductive parts of a flower, which comprises the sepals and petals.
Receptacle or thalamus is the fleshy part of the pedicel which holds the different parts of a flower, especially the androecium and gynoecium. They also form the fleshy parts of some false fruits like apple and strawberry.