There are multiple origins and meanings for the name:
1. Derived from the Slavic (Лето) meaning - "summer, summertime"
2. Latin given name, meaning - "killing"
3. Ancient Greek (Λητώ, Lētṓ; Λατώ, Lātṓ in Dorian Greek)
In Greek mythology, Leto was a daughter of the Titans Coeus and Phoebe and the sister of Asteria. The island of Kos is claimed as her birthplace. In the Olympian scheme, Zeus is the father of her twins, Apollo and Artemis, the Letoides, which Leto conceived after her hidden beauty accidentally caught the eyes of Zeus. Classical Greek myth records little about Leto other than her pregnancy and her search for a place where she could give birth to Apollo and Artemis, since Hera in her jealousy had caused all lands to shun her. Finally, she finds an island that isn't attached to the ocean floor so it isn't considered land and she can give birth. This is her one active mythic role: once Apollo and Artemis are grown, Leto withdraws, to remain a dim and benevolent matronly figure upon Olympus, her part already played. In Roman mythology, Leto's equivalent is Latona, a Latinization of her name, influenced by Etruscan Letun.