What does “girl next door” pretty mean?

It’s not an insult. It can mean a bunch of different things, it could be someone who is immensely pretty in a natural cute way (rather than beautiful), or someone who is very beautiful, but has a few “imperfections”. It can mean someone who’s cute in a really normal girl way. It often means women who look quite youthful/innocent and healthy (even if they are older). And it could mean someone who’s pretty in a natural appearing way. Usually by real life standards they’ll be some of the prettiest women around. Think Jennifer Aniston versus Angelina Jolie. Jen is stunning, but she’s got a slightly goofy nose and chin and especially when younger she had a slightly chipmunk face. But it adds to her charm, her minor “imperfections” make her both interesting and relatable. Angelina on the other hand is a much colder beauty, almost alien in her intensely “perfect” features. Also stunning, but not as relatable or attainable. They are such different beauties you can’t even compare them. By English standards, Kate Middleton is a “girl next door”. She’s stunning, but she’s not “perfect”, and that is one of the reasons she is considered so attractive. This aesthetic is highly coveted by men but often overlooked by women who tend to think a more Kardashian look is what’s desired. Many men tend to prefer more attainable looking women, and women who fit well within the girl next door aesthetic will usually have a lot of men chasing them. Part of this is that they appear attainable compared to many models/celebs so men might mistake them for being “average”, when by real life standards they’re top tier attractiveness.