Annie began as a diminutive of Anne (itself from Hebrew Hannah, meaning "grace"). It has been used as an independent name since the 18th century. The musical Annie (1977) about the spirited orphan kept the name in popular memory.
Annie was massively popular in the late 19th century, faded, and has returned in the 2020s. Today it sits in the U.S. top 400 — a small, warm, two-syllable name that wears well.
Annie reduces to five — the number of cheerful curiosity.