A robe worn by a Muslim woman is called an abaya or a jilbab, and men wear what is called a thwab. Generally, these robes are worn daily, over clothing.
An abaya is a cloak that covers the entire body and a jilbab is either a robe or cloak that covers every part of the body except for the hands and head. Many Muslim women choose to wear a headscarf or veil to accompany their robes.
Muslims dress in clothing that hides the body. The clothing is modest and most dress in earth tones to avoid drawing attention to themselves. They dress this way because in the "Qur'an," Allah directs his people to protect their modesty.