It can mean a lot of things really.
A delay in a period isn't unusual, it's quite common actually.
Some girls' periods arrive literally like clockwork while others might get theirs at slightly different times each month. But occasionally, a skipped period can happen during times of pressure or stress. It can also be because of the way you live. Maybe you decided to start working out more or you changed your diet. All of these things factor into a women or young girls period.