The word affair means an event or situation.

1. A fancy dinner party might be called a formal affair, meaning it's an elegant event where people dress up. When someone describes a wedding as quite an affair, they mean it was elaborate and impressive. The word suggests something significant or worth discussing.
2. A matter that concerns or involves someone. When adults say “that's not my affair,” they mean it's not their business or responsibility. Politicians debate foreign affairs (relationships with other countries) and domestic affairs (issues within their own nation). Your schoolwork is your affair, your responsibility to handle.