Intrauterine insemination (IUI): A procedure in which a fine catheter (tube) is inserted through the cervix (the natural opening of the uterus) into the uterus (the womb) to deposit a sperm sample directly into the uterus. The purpose of IUI is to achieve fertilization and pregnancy. IUI is a relatively simple procedure. "Intrauterine" is within the uterus. "Insemination" is from "in-" + "semen," seed = seed in. So, "intrauterine insemination" = seed in the uterus.