Do you mean "a form of marriage in which a woman has two or more husbands at the same time." (polyandry
This is part of polyamory... polyamory is an umbrella term for many different forms of consensual and ethical non-monogamy. If you do a tag search for "vee" "triad" "OPP" and anything else that catches your fancy, you will find others.... myself included.
Polyandry is illegal but if you mean a woman with two other men as lovers in a vee situation.... fill your boots, there are a lot on this site if you read around a bit.