Hair which we are forbidden to remove, which includes the eyebrows.
The action of removing the hair of the eyebrows is called al-nams. It is also forbidden to remove the hair of the beard.
The evidence for that is the hadith of ‘Abd-Allah ibn Mas’ud (may Allah be pleased with him) who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: “Allah has cursed the woman who does tattoos and the one who has them done, the woman who plucks eyebrows (al-namisah) and the one who has it done (al-mutanammisah), and the one who files her teeth for the purpose of beauty, altering the creation of Allah.” (Narrated by al-Bukhari, 5931; Muslim, 2125)
it was narrated that ‘Abd-Allah ibn ‘Umar said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: “Be different from the mushrikin: let your beards grow and trim your moustaches.” (Narrated by al-Bukhari, 5892; Muslim, 259)
al-Nawawi (may Allah have mercy on him) said:
“The namisah is the woman who removes hair from the face and the mutanammisah is the one who asks to have that done. This action is haram, unless a woman develops a beard or moustache, in which case it is not haram to remove it, rather that is mustahabb in our view.” (Sharh al-Nawawi li Sahih Muslim, 14/106)