A sty or pigsty is a small-scale outdoor enclosure for raising domestic pigs as livestock. It is sometimes referred to as a hog pen, hog parlor, pigpen, pig parlor, or pig-cote, although pig pen may refer to pens confining pigs that are kept as pets as well. Pigsties are generally fenced areas of bare dirt and/or mud. "Sty" and "pigsty" are used as derogatory descriptions of dirty, messy areas, the word sty deriving from the Proto-Germanic *stiją meaning filthy hovel. There are three contributing reasons that pigs, generally clean animals, create such a living environment:

• Pigs are voracious eaters and will eat all the plants in the enclosure until there is nothing left to control erosion.
• The pig will naturally root and dig for food in the enclosure, further disturbing the soil.
• Pigs do not regulate temperature by sweating which means that they must be provided with water or mud in which they can control their own body temperature.