That is for the number of post (response/comment) that you have made. Once you reach 100th post, you will earn the star rating.
200th post will give you a chances to use the emos
500th post, you can use cut and paste feature.
Thanks for the BR. Even though I thought it should goes to the below responder. He explain it correctly.
My first respond if for the number inside the bracket after your username and not for the star. Sorry for that.