When something's copacetic, it's fine. If you tell a classroom full of kids that they'll be spending the day at the beach instead of going to math class, they'll probably be copacetic with the idea.
When things are going well, they're copacetic. The adjective copacetic can describe the general mood of a group or gathering, a relationship between two people, or even the harmonies in a piece of music, with a meaning ranging from "just fine" to "excellent." Copacetic is considered an informal word, but it's been commonly used since around 1920. Its origins are unknown, but it's thought that it started in the 19th century in casual southern African American speech.