Can someone explain what 'girl next door' actually denotes? I've seen some people use it to describe girls who have a more innocent look yet others for girls who have the disposition of an unrealized succubus, and they can't both be right.

For example, was talking about Tom Cruise's love partners, and one suggested Katie Holmes as a girl next door, and another suggested his current partner, Ana de Armas, as the quintessential girl next door. Who is right? What does it actually mean?