Polygyny

Polygyny is a term for when a man has a relationship or marriage with multiple women. This could be due to culture or religious beliefs, but it is not required. Among cultures, polygyny is the most common and accepted form of polygamy. Polygyny is illegal in many Western countries, most of the countries that permit polygyny are Muslim-majority countries. In some countries where polygamy is illegal, polygyny is still a cultural norm.

It is in contrast to polyandry.

History
Polygyny has been around for centuries, forming amongst many cultures and taking place amongst animals in nature.

Flag
The polygyny pride flag was coined by Deviantart user NonMonoPrideFlags on December 3rd, 2015.

Resources
https://en.wikipedia.org/wiki/Polygyny#Cause_and_explanation