Friends who have each other's backs, look out for each other, spend lots of time together, and are just really good friends.
They have inside jokes together, they go to the park and swing on swing sets, get ice cream, go to the beach, go to concerts, go bowling, and basically any activity that they like doing together as friends.
1. Kaely and Xander are besties!
2. Kaely: Yesterday, I went to the park and played on the swings with Xander!
Sam: Well of course! You're besties!