1) Lesbianism 2) Sapphism 
Tribadism (əm {respell|TRIB|ə-diz-əm}) or tribbing, commonly known by its scissoring position, is a form of non-penetrative sex in which a woman rubs her vulva against her partner`s body for sexual stimulation, especially for ample stimulation of the clitoris. This may involve female-to-female genital contact or a female rubbing her vulva agai....
lesbian intercourse in the missionary position
Lesbianism, particularly as practiced by a tribade. ... Origin: G. Tribo, to rub ... (05 Mar 2000) ... 
noun a form of lesbianism that simulates heterosexual intercourse