Learner's definition of CASUAL
1 always used before a noun : happening by chance: not planned or expected 2 [more casual; most casual] : designed for or permitting ordinary dress, behavior, etc.: not formal
◊ Casual days are days (such as casual Fridays) when a company allows workers to dress in casual clothes.
[more casual; most casual]
3 a : done without much thought, effort, or concern b : not involving a close or serious relationship c : having some interest but not a lot: not serious 4 : happening at certain times but not on a regular basis