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.
(..) Relationship Agreement, on the anniversary of our first date, he must take me to a nice dinner, ask about my day and engage in casual physical contact that a disinterested onlooker might mistake for intimacy. That's hot. You kids better use protection. (..)2012 TvShow: The Big Bang Theory Title: The Date Night Variable Season: 6 Episode 1
(..) on your date night with Amy? Oh, absolutely. I have a contractual obligation to provide Amy with conversation and casual physical contact, but nowhere is it specified that I can't outsource that to an Indian. BERNADETTE: (..)2012 TvShow: The Big Bang Theory Title: The Date Night Variable Season: 6 Episode 1
(..) on the Iron Throne. Join us. Together, we can end her tyranny." Sounds like a charmer. Of course, the casual mention of a Dothraki horde, a legion of Unsullied, and three dragons... a bit less charming. What? (..)2017 TvShow: Game of Thrones Title: Stormborn Season: 7 Episode 2