A porno is a pornographic movie, a type of film featuring sex and only meant to excite people sexually.
Like romantic comedies, science fiction, westerns, thrillers, and cartoons, a porno is a type of movie — specifically a dirty movie featuring people having sex. Pornos don't have much plot or artistic value: they show sex and are meant to get people in the mood for sex. Many moves have sexual elements but aren't considered pornos. A porno has sex and not much else that would make it worth watching.
