There are several types of disc jockey. Radio DJs or radio personalities introduce and play music that is broadcast on AM, FM, digital or Internet radio stations. Club DJs select and play music in bars, nightclubs or discothèques, or at parties or raves, or even in stadiums. Mobile DJs travel with portable sound systems and play recorded music at a variety of events. Some mobile DJs also serve as the master of ceremonies (MC) at weddings or other events, directing the attention of attendees, and maintaining a room-wide focus on what is included in the event's agenda.