In biology receptacle is the swollen basal part of the flower or can also be geared a's the top of the stalk or pedicel. When the stalk of the plant (The part which connects flower to the plant) gets flattened and the other parts of the flower including the 4 whorls (calyx,corolla,androecium,gymnoecium) start that flattened part is called the receptacle.It is the end part of the stalk or pedicel.
In some fruits like the strawberry it is the thing which becomes the main fleshy edible part of the fruit.The fruit specie rubus has a conical receptacle with a cluster of seeds (droplets) on top of it.
When a raspberry is picked the receptacle gets separated from it but it is just the opposite case in blackberry where it remains attached.
In psychology they are the structures at the end of the branches of algae mainly brown algae. There they act as specialized structures having reproductive organs and also help in storage.