What do bindis stand for? Can some Indians help, pls?

Tweet

Hey guys, I am wondering what does a bindi stands for? Bindi are the dots or markings in the forehed, some are inbetween the eyebrows. Can any one explain what is it for? Some are very decorative ones, like diamonds and some are colorful. Are they just for accessories? Can any one just wear them like me? I'm no Indian. I would appreciate if you guys could shed some light on this. Thanks ahead.