Basically an illusion. People say they're popular just to get attention and make themselves seem better than they actually are. These "popular" people will throw parties and wear expensive clothing to look "cool" Stupid people who also want attention and to seem better will start worshiping them.
Girl 1: OMG she's so popular. I want to be just like her!
Girl 2: You know, most people don't actually like her. She only THINKS she's so cool. Take a look around for once.
Girl 1: but...but...but...