may use chord charts or sheet music or no music notation at all, which is typically the case at a session with experienced participants and/or professionals. In sessions where no music notation is used, the participants or leader "call" well-known tunes that the other performers know "by ear", either by stating the title aloud, or more simply by starting into the melody. Jazz and blues In jazz and blues (and related genres and subgenres), a session is typically called a jam session or a jam. Jam sessions often take place after musicians and singers have finished their paid gigs for the evenings. Jams often take place at nightclubs or bars. Jams may include both professional instrumentalists and singers and talented amateurs. Some venues have a "house band" or backing band, a paid rhythm section that includes one or two chordal instrumentalists (e.g., piano, Hammond organ, electric guitar, etc.), a bassist (e.g., electric bass or double bass) and a drummer. In jazz, jam participants include "horn players" ("horn" in jazz parlance means any of the wind or brass instruments used in the genre, including saxophone, trumpet, trombone, etc), rhythm section instrumentalists (who typically "sit in for" or replace one of the house band members) and singers. At more amateur jazz jam sessions, the performers may use lead sheets that contain the chord progression and melody of the song in music notation or fake books. At a more professional jam, performers may simply "call out" tunes, with the performers being expected to know the melody and chord changes. At a blues jam, the session performers may include electric guitarists, harmonica ("blues harp") players and singers. At blues jams, the house band typically plays twelve bar blues and other blues song forms that are well-known for the session participants to solo over. At blues jams, the guitar solo, typically played on electric guitar through an overdriven guitar amp, is an important type of solo. Role of leader Paid session leaders help to ensure that there will be music performances throughout the evening for members of the public who might wish to listen without participating. The leader also acts as a host and master of ceremonies for the event, introducing performers and, thanking them after their songs and calling for applause. The session leader selects players and singers who are skilled enough to deserve a solo performance, and politely asks inexperienced performers to wait