this article is mainly not about justification of explanation of what is known as polygamy in islam, it is meant to reach a precise definition of  the islamic permission of a man to have more than one wife in a certain term , which inaccurately used to be described as " polygamy in islam";  we need to define and analyze the term "polygamy" first lexically, historically and anthropologically; then narrow our attention to focus at the islamic case. thus we can come out with a true understanding of the case in islam and how far could it be referenced to as polygamy. let's start, as mentioned, by definition and analysis of polygamy which contains some details that you might see of no use; but by the end of this how much they are relevant to the subject.

polygamy is defined as having more than one spouse wife or husband at the same time . polygamy differs from bigamy which is considered the crime of marrying during the continuance of a lawful marriage. often in a polygamous marriage, a man marries sisters or the daughter of a wife. throughout history many societies have condoned or accepted plural marriages, another term for polygamy, as referenced by the us history encyclopedia. 

polygamy broadly entitles two independent terms:

the first is polygyny which describes a marriage form in which a man has two or more wives at the same time. the bible mentions approximately forty polygynists, including such prominent figures as abraham, jacob, esau, moses, david and king solomon. polygyny has been practiced in many cultures throughout history. it was accepted in ancient hebrew society, in classical china , and in many traditional african and polynesian cultures. in india it was practiced during ancient times. it was accepted in ancient greece , until the roman empire and the roman catholic church when having one wife, but multiple lovers became the usual. historically, polygyny was used in some societies to enhance certain genetic characteristics, and to weed out unhealthy characteristics. they even encouraged polygyny due to the asymmetric reproductive ability between men and women, wherein men are physically capable of producing many more offspring than women. moreover, owing to the propensity of men to serve and die in wars or labour incidents^, women, for centuries, were more likely than men to be left unmarried or widowed. polygyny ensured that such women were cared for and also helped ensure the births of the large numbers of children required for the survival of pre-mechanized, largely-agrarian cultures in which early mortality rates were high. it has always been suggested that in a polygynous structure, jealousy between co-wives over perceived unequal attention from or access to their shared husband is common.  such societies came out with sororal polygyny in which two or more sisters share a husband as a solution assuming that sisters would be more likely to amicably share a husband.

the second is polyandry which describes a marriage form in which a woman has two or more husbands at the same time. polyandry in human relationships occurs or has occurred in tibet, the canadian arctic, nepal, bhutan, parts of india (ladakh, zanskar), the nymba, and sri lanka, and is known to have been present in some pre-contact polynesian societies, though probably only among higher caste women. it is also encountered in some regions of mongolia , among the mosuo people in china , and in some sub-saharan african such as the maasai people in kenya and northern tanzania and american indigenous communities. polyandry has been practiced in several cultures in india — in the jaunsar region in uttarakhand, among the, nairs, theeyas and toda of south india, and the nishi of arunachal pradesh. the guanches, the first known inhabitants of the canary islands , practiced polyandry until their disappearance. in other societies, there are people who live in de facto polyandrous arrangements that are not recognized by the law. there are no known indigenous communities that currently practice polyandry involving unrelated males. polyandry is a controversial subject among anthropologists. for instance, anthropologist stephen beckerman points out that at least 20 tribal societies accept that a child could, and ideally should, have more than one father, referring to it as "partible paternity". most traditional societies have been drastically altered or destroyed, so the incidence of polyandry in the past may not be accurately known. in india , among tibetan refugee groups who fled the chinese takeover of their country, polyandry is seldom encountered.

after this brief analysis; whoever says that " polygamy is permissible in islam" the sentence accordingly should mean that what is mentioned above is mostly if not totally applicable to islam which is totally wrong. neither polygamy; with its' broad meaning , nor polyandry are permitted in islam, on the contrary; they are forbidden. so the closest term to the islamic case is polygyny, but in islam it is a very special type of polygyny. marriage in islam is mainly monogamous; but as islam is the religion for every people at every time till the day of resurrection, and as allah is the creator of humanity and "he knows the treacherous (look) of the eyes and whatever the breasts conceal" (ghafir :verse 19), he set the regulation for each motion and each act of any human being till the end of time. in certain cases, a man needs to have another woman in his life, while keeping his current wife, or a woman might need to get married or have a husband after her ex or late husband and no one can deny such feelings and needs within humans. it is clearly apparent through history and anthropology as hinted before. though this article is not about justification of the matter in islam; but the late words had to be said.

in islam there is no acceptable relationship between a man and a woman; foreign from each other, but marriage. with certain regulations and conditions; man can have more than one wife. as polyandry is forbidden in islam, our minds should now jump to describe the case as polygyny, but not all the mentioned about polygyny is acceptable in islam. if polygyny is to be practiced, some regulations and conditions should occur. for instance, the man involved should has both the physical and financial ability, he should be quite sure that he will treat them equally, he must not marry more than four wives simultaneously, he must not marry the daughter of his wife, he must not marry two sisters at the same time, and other conditions which are not mainly the subject of this article. so we can best describe the case in islam as "conditional or regulated polygyny".

in conclusion, what ever the discussion is about, it is about thinking and reasoning; which are both judged by the words imply to each point of view. the precision and clarity of terminology is urgent to communicate what we really have in mind with others who might have different cultures, thoughts, stereotypes and, as a result, different interpretations of the terms we use, which might lead to some misunderstanding  that cannot be tolerated regarding religion.

to know more about the regulations of polygyny in islam, read:

http://www.old.rasoulallah.net/subject_en.asp?hit=1&lang=ar&parent_id=29&sub_id=6149