Zekeinah literally means old woman. Much of the halachic discussion of this concept does not include a specific age but rather refers to an age at which a woman wouldn't mind being referred to as elderly or a grandmother. One source, Shu"t Panim Meirot 12, lists the age of 53.

In the context of the laws of family purity, it is the age from which a cessation of menses for over ninety days exempts a woman from observing onot perishah. In other words, a fifty-three year old woman who goes ninety days without becoming a niddah does not have any obligations to perform a bedikah or separate from her husband on the days when she would normally anticipate her period. She is halachically considered to have reached menopause.

A woman retains this status unless or until she either becomes niddah three more times, or she becomes niddah on the day of her former veset kavua.

In contrast, a woman who reaches menopause at an earlier age would observe onot perishah from the first time she might happen to become niddah again.

As other factors may enter into the discussion if a woman has to observe the onot perishah, we suggest that an individual question be asked in each case.