Outside Iran the chador is often treated as the Iranian version of the hijab. Inside Iran it is one option among several, and which one a woman wears is read as a statement.
The legal minimum is a covering of hair and body shape, and the ordinary urban solution is a manteau, a coat, worn with a roosari, a headscarf, often pushed well back. The chador is a further step: a full length semicircle of cloth held closed at the front, usually with the hands or the teeth, worn over the other clothes. Black is the public form. There is also a printed floral chador worn at home and in the provinces, and a light chador-e namazi kept for prayer, so a woman who never wears a black chador in the street may own two others.
Wearing the black chador in public is generally read as a declaration of religious seriousness or of political alignment, and it is required for entry to certain shrines and offices, where loaner chadors are provided at the door.
The garment predates Islam in Persian dress and appears in accounts of pre Islamic Iran. Its modern history runs in both directions within one lifetime. Reza Shah banned it in 1936 and had police remove it forcibly from women in the street, an episode that kept some women indoors for years and that is remembered with bitterness by religious families. After 1979 covering became compulsory, enforced by law and by a morality patrol, and the chador became state approved dress.
A woman old enough could therefore have been unveiled by force in one decade and veiled by force in another, by two governments of the same country, both claiming to act in her interest.