What term refers to the surgical removal of one or both testicles?

The term that refers specifically to the surgical removal of one or both testicles is "orchiectomy." This procedure is often performed in male animals as part of sterilization and helps to prevent unwanted behaviors associated with mating, as well as reducing risks of certain diseases. Orchiectomy can be performed on pets like dogs and cats to control the population and improve health outcomes.

While "neuter" is a broader term that encompasses any surgical process aimed at sterilizing an animal, including both orchiectomy and spaying (the removal of ovaries and uterus in females), it does not specify the removal of testicles alone. "Spay" is related to female animals and does not pertain to the surgical removal of testicles. "Euthanasia" refers to the process of intentionally ending an animal's life, typically to relieve suffering, which is unrelated to the surgical removal of reproductive organs.