Something the girls in the example pictures aren't.

Someone who YOU find attractive. Someone who in your opinion is appealing. This person may not seem "Sexy" to others, but to you they are the definition OF sexy.

People saying that the girls in the example pictures aren't sexy, are not getting what sexy means. To you they may not be sexy, but, to someone they could be the most beautiful, sexy, hott thing EVER.

Supposed to mean sexually attractive, however recently it has become a word of ambiguous meaning that morons use when unable to think of a better adjective for something they like.

The most amazing version of hott.
Usually a stunning girl not only with her body, but the way she acts.

Noun - My Baby Anna, I love you puppy

A person that is pleasing to the eyes and is appealing.

someone who makes you want to do bad things to them

An adjective to describe a person you think is really attractive and want to have a physical relationship with.
But it mostly depends on perspective. Someone may think a person is sexy while the person next to them totally disagrees.