"Verabredung" basically means that you agree with someone on something. That can be some kind of deal or informal contract (Vereinbarung), but very often you agree on a certain time when you want to meet up with someone. That can be a date (with your (not yet) girlfriend/boyfriend), or an appointment to go out with friends. It's never a "formal" appointment with a doctor, or in a business sense. That would be a "Termin" (Arztermin, Geschäftstermin). Today people also often use the English word "Date" if they are going to meet with their boyfriend/girlfriend: "Ich hab' heute abend 'nen Date, ich kann nicht zu der Party kommen.".

Ich stimme Dirk zu und würde fast so weit gehen und sagen, dass ich persönlich fast nur noch "Date" zu einer romantischen Verabredung sage und "Verabredung" für mich eher neutral ist. Im professionellen Umfeld wie gesagt "Termin".