Chasidei Umos HaOlam
Chasidei Umos HaOlam is the hebrew term used by Maimonides in the Laws of Kings 8:11. It is generally translated as "Righteous Gentile" or more recently "Observant Noahide". It indicates a non-Jew who has taken upon himself the observance of Noahide Law, and does this because it was revealed through Moshe Rabbenu as explained by Jewish tradition. According to Maimonides, Chasidei Umos HaOlam are assured a portion in the world to come. This is something that is not assured for the Chochmei Umos HaOlam who observe Noahide Law, but do it for their own rational reasons.
The Aramaic scriptures refer to them as מסלם.