Seeds have a protective covering around them which prevents them from desiccation and have an adequate amount of food supply.
Seed along with its protective covering and food supply is referred to as fruit.
The fruit of the palm tree, double coconut, also known as Lodoicea maldivica or coco-de-mer is known to produce the heaviest and the largest seeds in the world.
The seeds of this plant can weigh about 15 kgs and 12 inches.