A sty or pigsty is a small-scale outdoor enclosure for raising domestic pigs. It is sometimes referred to as a hog pen, hog parlor, pigpen, pig parlor, or pig-cote. Pigsties are generally fenced areas of bare dirt and/or mud. "Sty" and "pigsty" and "pigpen" are used as derogatory descriptions of dirty messy areas. 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 is a rooting animal and will 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.