What does hijab actually cover?

It's an outfit, not just a scarf

In everyday English, "hijab" means the headscarf. In Islamic law, it means the whole way a woman covers. A headscarf with a tight, short top doesn't fulfill it; a loose, long outfit with a scarf that covers the hair, neck and chest does.

Face and hands

The Quran allows "that which [necessarily] appears" of a woman's adornment (Quran 24:31). Many early scholars, including Ibn Abbas, explained this as the face and hands. A hadith in Abu Dawud also reports the Prophet ﷺ pointing to the face and hands as what may show after puberty (Sunan Abi Dawud 4104). Abu Dawud noted a gap in its chain, but scholars such as al-Albani accepted it through supporting reports.

• Hanafi and Maliki: face and hands may show.
• Many Hanbali and later Shafi'i scholars: the face should also be covered in front of non-mahram men.
• Feet: most schools say cover them; the Hanafi school says they may show.

See Is niqab required in Islam? and Do I have to cover my feet as a Muslim woman?

Three simple conditions

• Covering: the areas above are covered.
• Loose: clothes don't show the shape of the body.
• Opaque: no see-through fabric.

Scholars also mention that it shouldn't be designed to attract attention, and shouldn't be specifically men's clothing. See Can I wear tight or see-through clothes with hijab?

When it applies

Hijab applies in front of men who aren't your mahram (close relatives you can never marry) or husband. At home with family and among women, you can relax much of it. It also applies in prayer, even when you're alone. See Who can see me without my hijab?