Allah tells us in the Qur'an:
وَقُل لِّلۡمُؤۡمِنَـٰتِ يَغۡضُضۡنَ مِنۡ أَبۡصَـٰرِهِنَّ وَيَحۡفَظۡنَ فُرُوجَهُنَّ وَلَا يُبۡدِينَ زِينَتَهُنَّ إِلَّا مَا ظَهَرَ مِنۡهَاۖ وَلۡيَضۡرِبۡنَ بِخُمُرِهِنَّ عَلَىٰ جُيُوبِہِنَّۖ وَلَا يُبۡدِينَ زِينَتَهُنَّ إِلَّا لِبُعُولَتِهِنَّ أَوۡ ءَابَآٮِٕهِنَّ أَوۡ ءَابَآءِ بُعُولَتِهِنَّ أَوۡ أَبۡنَآٮِٕهِنَّ أَوۡ أَبۡنَآءِ بُعُولَتِهِنَّ أَوۡ إِخۡوَٲنِهِنَّ أَوۡ بَنِىٓ إِخۡوَٲنِهِنَّ أَوۡ بَنِىٓ أَخَوَٲتِهِنَّ أَوۡ نِسَآٮِٕهِنَّ أَوۡ مَا مَلَكَتۡ أَيۡمَـٰنُهُنَّ أَوِ ٱلتَّـٰبِعِينَ غَيۡرِ أُوْلِى ٱلۡإِرۡبَةِ مِنَ ٱلرِّجَالِ أَوِ ٱلطِّفۡلِ ٱلَّذِينَ لَمۡ يَظۡهَرُواْ عَلَىٰ عَوۡرَٲتِ ٱلنِّسَآءِۖ وَلَا يَضۡرِبۡنَ بِأَرۡجُلِهِنَّ لِيُعۡلَمَ مَا يُخۡفِينَ مِن زِينَتِهِنَّۚ وَتُوبُوٓاْ إِلَى ٱللَّهِ جَمِيعًا أَيُّهَ ٱلۡمُؤۡمِنُونَ لَعَلَّكُمۡ تُفۡلِحُونَ (٣١)
Translation (interpretation of meaning):
And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (ordinarily) appear thereof; that they should draw their veils over their bosoms and not display their beauty except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, or their brothers' sons, or their sisters' sons, or their women, or the slaves whom their right hands possess or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! Turn ye all together towards Allah that ye may attain Bliss. (31)
Surat 24 Ayah 31
Emphasis mine.
Not that I doubt the Ayah or the Hadith, but a translation into English will always be limited compared to when it is in it's original language so I don't know how articulate the translation is of this section;
...they should not display their beauty and ornaments except what (ordinarily) appear thereof and that they should draw their veils over their bosoms and not display their beauty except to their husbands.
Here, what does Bosom mean? Chest, torso, upper chest, neck?
What is the original intention?