A female pig is called a sow. This term is commonly used to refer to an adult female pig that has given birth to piglets. The word "sow" specifically denotes a female pig that is capable of reproducing. The other options, such as boar, piglet, and piggy, do not accurately describe a female pig. A boar is a male pig, a piglet is a young pig, and piggy is a colloquial term that can refer to either a male or female pig.