Wa ‘Alaykum al-Salam wa Rahmah Allah wa Barakatuh

And upon you be peace, and the mercy of Allah and His blessings; the full reply to the greeting of peace

What it means

This is the full reply to al-salāmu ʿalaykum, “peace be upon you”. It means: “And upon you be peace, and the mercy of Allah and His blessings.” The shortest reply is wa ʿalaykum al-salām, and the longer form adds a prayer for mercy and for blessing. The Quran tells the believer: “When you are greeted with a greeting, answer with a better one, or at least return it” (4:86). Jurists therefore treat the return of a greeting as a duty. The exchange of greeting is a mark of Muslim fellowship, and it is the first words spoken when two Muslims meet.

Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 59, listed as WA ‘ALAYKUM AL SALĀM WA RAḤMAH ALLAH WA BARAKĀTUH.. The definition is restated here.