The word "really" is an adverb used to emphasize the truth or reality of something. It can express surprise, intense confirmation, or a degree of seriousness in a statement. When someone uses "really," they often want to stress that what they are saying is genuine or significant.
The word "really" comes from the Middle English "reallich," which means "genuinely." This term is derived from the Old French "reel," meaning "real" or "actual," which in turn comes from the Latin "realis," meaning "actual, real."