Spaying and neutering are both procedures used to sterilize animals like dogs and cats, but spaying refers to the procedure done to female animals while neutering is the corresponding process for males. Spaying involves taking out the uterus and ovaries while male pets are neutered by taking out the testicles.
Due to high levels of feral cat and dog populations in both developed and developing countries, it is often recommended to have pets sterilized to keep the animal population in control. People can rescue an animal from the shelter instead of buying one from the litter of an animal that already has a home. Animal services and shelters often spay and neuter any pets that are taken in off the street.