This question popped up to my mind and it is inspired by the previous post (What is Love?).
Beauty is an interpretation of some kind of love or let me say liking. When we see something we like, we say its beautiful. Defining the word “like” will take another post, so I will stick with the word “beauty”.
When we see a person who is beautiful, it means that we either love this person, so we like everything about this person, then he/she becomes the most beautiful person in the world. Or we like something about this him/her, so it could be the shape of his/her face, the color of the eyes, or his/her hair cut/style. People sometimes look beautiful for the way they dress and depending on your mood.
If you notice, sometimes you see a beautiful person, and another day, they are just like the rest, the beauty is just gone. It could be that she/he was wearing something you like.
This word has a very complex meaning, I tried to express it in my own simple words.