What is the ruling on saying "Amen" after reciting Surat Al-Fatihah outside of prayer?

Saying "Ameen" (Amen) is a Sunnah after finishing Surat Al-Fatihah, whether in prayer or outside of it. It is Sunnah for both the Imam and the congregant to say it aloud in audible prayers and silently in silent prayers. It is a supplication meaning "Respond, O our Lord."