According to the Wiktionary, mineral makeup is essentially a cosmetic product that is formed from very finely ground minerals, mixed with a base compound for cohesion, such as cocoa butter. Mineral makeup has many similarities to powder foundation, and they are sometimes interchangeable.
Employing mineral makeup is a highly regarded method of accenting one's own natural beauty. Often times, these cosmetics will not contain synthetic colors/dyes, such that your "true colors" will show. Using a base foundation that more accurately matches your natural skin tone is also an effective means to looking healthy, rather than simply dolled-up.
Applying an organic makeup from mineral elements is also great for an everyday look, whether it be for school or work.