"Rectal temperature" refers to a method of measuring body temperature using a thermometer that is placed in the rectum, which is the end part of the digestive system. Full definition
A research team led by Maddie's Shelter Medicine Program at the University of Florida professor Dr. Julie Levy measured rectal temperatures of 200 healthy cats in homes, shelters, and veterinary hospitals. (sheltermedicine.vetmed.ufl.edu)
You can take rectal temperature using a digital thermometer or an electronic ear thermometer for taking temperature through the child's ear canal. (newkidscenter.com)
Read more and find links to the studies at Reference interval for rectal temperature in healthy confined adult cats. (sheltermedicine.vetmed.ufl.edu)