Emerson is an English surname meaning "son of Emery" — Emery from the Old Germanic Amalric, meaning "work-ruler." The name became associated with the American philosopher Ralph Waldo Emerson (1803-1882), one of the founders of Transcendentalism.
Emerson as a girl's first name is recent — it entered the U.S. top 1000 in 2003 and has risen rapidly. Today it sits in the U.S. top 100 and is used about 70% for girls.
Emerson reduces to three — the number of literary expression.