clear evidence / clear proof
Feminine adjective used as a noun (فَعِّلَة pattern). Related: بَيَّنَ (to make clear), بَيَانٌ (clarity/eloquence), مُبِينٌ (clear/manifest), تِبْيَانٌ (clarification). An entire surah is named Al-Bayyinah (98).
Al-Bayyinah (the Clear Evidence) refers to the Prophet Muhammad ﷺ or the Quran itself. Islam emphasizes that God provides clear evidence before holding people accountable.