1. Chill and relaxed yet sophisticated and classy. Often referring to a state of being, way of life, or way to dress.
2. To be awesome while at the same time not caring at all.
Dave: Dude, that bbq and ladder ball with the bros was a great time.
Jake: Yeah dude, it was so casual.
Sam: Dude...the Vineyard Vines oxford/seersucker shorts combo is totally casual