The word has never been defined as such, however. The term Reploid/Repliroid refers to robots created with the ability to think and reason on a Human level.
From the Zero collection timeline:
"Reploids… those are robots made a time long ago who were near human and had limitless potential… Given individuality by means of advanced technology, the Reploids worked for humans and were meant to be the greatest ally to walk alongside mankind…
And from the same site, the profiles, on X in particular:
The Legendary Blue Messiah" X
The legendary blue repliroid and ruler of Neo Arcadia who symbolizes "infinite potential" and a "purveyor of justice" for all.
The term is used to refer to any advanced Robot with Human level intelligence. It was never used to refer to replication.
Also, like ive said before, Reploids are not Replicas of X. the Black Copy Zero, is a replica. Nightmare Zero, is a Replica. (clone, to be more precise, but you know,) Copy X, is a Replica. Zero's Copy body in the Zero series, is a Replica.