it is called menstration.
Every female has some discharge. It's the vagina's way of cleaning itself. Expect a quarter to a half teaspoonful of milky-looking fluid every day, which sometimes dries slightly light yellow or light green on the underwear. At mid-cycle, this will turn clear, stretchy and thick, like raw eggwhite. Don't worry, it's all quite normal. The only time you would need to do anything about it is if it gets thick and white like cottage cheese. Then it might be a sign of a yeast infection. In the meantime, if it bothers you, wear a small pantyliner.