The Greek word for romantic love, as distinct from philos and agape. It is love in the sexual sense, a physical and desirable attraction between two people.
It's not the same as infatuation, which is temporary and easily forgotten when a distraction arrives. Rather, it speaks of the physical and emotional attraction between two people. It could be considered synonymous with "lust", but that's a negative term and not used in the same spirit. Lust is just wanting to have sex with someone. Eros is more like making love, which, as anyone who has known both will tell you, is like the difference between night and day.