To tell you the truth, I've never really thought about what make-up was to me. When I was 12, it was some God-like substance that kids with "cooler" moms lets their children dabble in, something that was to be revered and wondered and whispered about. When I was 13-14, it was something to be sneered at, a false, often ugly mask that the popular girls sported. I hated it at that point, along with fashion and general girlishness.
Of course, I'm older now and very much into the fashion/cosmetics world. I've spent a good amount of time playing with my powders and brushes and liners, figuring out how everything felt on my face, and how it made me look. I've honed in on my own beauty, and grown comfortable with my appearance. But still, I had never really considered what make-up was. Now, however, I've come to realize it's not just one thing.
Make-up starts as a tool. Humans use it to adorn their bodies and fix things about themselves that they do not like. Its a way to fit into the mold that we, as a society, create. However, make-up has also transcended that role much in the same way clothing has. Its become something that people fall in love with. An art-form, as many have called it. Its a way to show yourself in a sometimes subtle, sometimes not, way. Its both self-expression and a means of hiding insecurities. Its liquid/powder courage. Its a way to remember styles and people long gone. And, on the uglier side, it is a way for big companies to make money by exploiting the negative feelings of both men and women. Its a means of animal cruelty. Its a way to distinguish which kind of people you do or don't want to know. Its a way of attracting a mate. Its something to shamefully spend a ton of money on when there are humans who don't even have clean water.
So, to try and answer the question of 'what is make-up to you?', there can be no one answer. Make-up, simple pigment transformed into powders, goops, and liquids, is more like an idea. There can be so many things wrapped up into it. Sure, it is a tool to be used, but it also moves, infuriates, and delights people.