A male pig may be called a boar, barrow and stag. These gender specific terms are often used for swine that are raised as livestock. Gender specific terms for female swine raised as livestock are sow and gilt.
In pig farming terms, a boar is a male pig that is used for breeding. A barrow, on the other hand, is a male swine that is castrated even before it reaches maturity. A male swine that is castrated after it has been used for breeding purposes is called a stag. The term "pig" is often reserved for a young, immature swine in swine farming and it is synonymous with shoat, nursery pig, and grow-finish pig.
Gender-specific pig farming terms for female swine include sow, which is used for a swine that has farrowed her first litter and gilt, which is a term used for females who have yet to breed.
Modern breeds of pigs are believed to have descended from the Eurasian wild boar. The domesticated pig is one of the most numerous large mammals on the planet and their numbers are estimated to be approximately one billion. In the wild, pigs are omnivorous foragers and are highly adaptable. They are such successful breeders in the wild that they have become an invasive species in areas where they are introduced, severely altering the ecosystem.