1. A version of "pretty" or "handsome" that works for everybody.
2. Someone who is pretty in a very generic way.
They may be generally agreed upon (in their culture) as pretty or handsome, but they do not stand out in any way. There is nothing striking about their beauty.
If you were to do a
composite of all the features men or women find to be attractive and create a computer-generated image of it, this is who would pop out.
The term comes from the idea that
catalog and underwear models must not
overpower the clothing that they wear and thus those who cast them pick the most mainstream-looking of the models. Consequently, underwear models all look very similar to one another in a very striking way.