Mating is the pairing of opposite-sex or hermaphroditic organisms, usually for the purposes of sexual reproduction. Some definitions limit the term to pairing between animals, while other definitions extend the term to mating in plants and fungi.
For some hermaphroditic species, copulation is not needed because the parent organism can self-fertilize (autogamy). In some flowering plants self-pollination can happen within the same flower, and some hermaphrodite animals self-fertilize. Many gastropods are hermaphrodite, and do simultaneous copulation. So do earthworms.