When an average or ugly person befriends an attractive popular person for the sole purpose of making themselves look and feel attractive. In some cases, the person may even start to think he/she themselves look attractive when in reality, they're not. An attractive person may use this as an advantage as well to make themselves look better by befriending a lesser attractive person, so they don't come off as shallow.
"Hey, Maegan's at it again. She always follows Lily around."
"G'yeah, she's definitely Lily's Booster Buddy."
"Oh god, look at her fat thighs, she shouldn't wear shorts."