“…and do not display yourselves [tabarruj] like that of the times of ignorance…”
This is one of the good manners which Allah s.w.t. enjoined upon the wives of Rasulallah s.a.w. as an example for the women of the ummah to follow.
Of tabarruj, Mujahid said: “Women used to go out walking in front of men, and this was the Tabarruj of Jahiliyyah.” Qatadah said: “When they go out of their homes walking in a shameless and flirtatious manner, and Allah, may He be exalted, forbade that.”
Muqatil bin Hayyan said: “Tabarruj is when a woman puts a khimar (head covering) on her head but does not tie it properly.” So her necklaces, earrings and neck, and all of that can be seen. This is Tabarruj, and Allah addresses all women of the believers with regard to the prohibition of Tabarruj.
[Tafsir Ibn Kathir]