It's another way of saying spaying. Queens (female cats) and bitches (female dogs) are spayed and dogs and cats (both males) are neutered.
I have a cat and two dogs, she's spayed and they both are neutered. Spaying and neutering are not only good to reduce the number of unwanted pets, but it can also eliminate or reduce the incidence of health problems, thus allowing them to live longer and healthier lives.
I know it means neuter, I just couldn't resist the joke!!