They are only 'casual' acquaintances. [=they know each other but not very well]
She takes a 'casual' [='nonchalant'] approach to her homework.
He was dressed 'casually' in jeans and a sweatshirt.
(..) We were supposed to meet up at her place later that night... but she never showed up. You didn't text her or ask her why? It was casual. Sometimes we would meet up, sometimes plans would change. If it was so casual, (..)2015 TvShow: Bones Title: The Promise in the Palace Season: 11 Episode 7