What is meant by sweet 16?

ok, right i find myself ugly at the moment, and i was just wondering what is meant by sweet 16 ? is it when a girl leaves the ugliness and turns into pretty ! is this true? because i want ways to find myself to be really pretty and all that , so that people can notice me and say wow shes pretty. i look at my freinds and think wow shes really pretty i wish i could be like her, i want people to do the exact same with me but i also want information about sweet 16 AND prettyness thanx xxxx ;)