Polygamy is the broader term used for both polygyny and polyandry. So polygamy is two or more women married to one man or vice versa
However polygyny specifically is when one man marry two or more women at a same time. Which is conditionally permissible in Islam
Polyandry is the opposite of polygyny in which one woman marries two or more men at a same time. This tradition Is found in some underdevelop part of South India