Copulation is a word for sex: specifically, the penis going into the vagina kind of sex.
Copulation is an even more scientific way of saying "sexual intercourse." You can use this word to describe the sexual practices of both humans and animals. Zoologists need to make sure there is copulation among endangered animals such as pandas. Stray animals like cats engage in a lot of copulation, which is why there are so many cats. If your female dog is not fixed and copulates at the park, you might have puppies on the way soon.