In Islam, iddah or iddat (Arabic: العدة‎; period of waiting) is the period a woman must observe after the death of her husband or after a divorce, during which she may not marry another man. One of its main purposes is to remove any doubt as to the paternity of a child born after the divorce or death of the prior husband.
The length of ‘iddah varies according to a number of circumstances. Generally, the ‘iddah of a woman divorced by her husband is three monthly periods, but if the marriage was not consummated there is no ‘iddah. For a woman whose husband has died, the ‘iddah is four lunar months and ten days after the death of her husband, whether or not the marriage was consummated. If a woman is pregnant when she is widowed or divorced, the ‘iddah lasts until she gives birth.
Islamic scholars consider this directive to be a balance between mourning of husband's death and protecting the widow from criticism that she might be subjected to from remarrying too quickly after her husband’s death. This is also to ascertain whether a woman is pregnant or not, since four and a half months is half the length of a normal pregnancy.