A pup.
The mother looks after and provides milk for her offspring.
A swine offspring is called a piglet.
A canine offspring is called a puppy.
Offspring of ducks are called "ducklings" and that of geese are called "goslings."
A male seal is called a bull
A Mares' offspring is called a "Foal".
Pigs offspring are called piglets.
A female seal is a cow.A male seal is a bull.A young seal is a cub.
....an old elephant seal! I don't think there's any special name for elderly seals or sealions. Males and females are called bulls and cows, and their offspring are known as calves or pups, but I don't believe they aquire any special title due to their advancing age.
The offspring of different animals are known by different names- for example the oppsring of a Lion is called a cub, that of a cow is called a calf and so on.
The visible trait an offspring exhibits is called the phenotype.
The passing of traits from parents to offspring is called heredity.