Definition of aftershow in English:

aftershow

noun

Music Theatre
  • (Chiefly Theatre and Music) a subsequent or additional performance; (now especially) an impromptu or unadvertised rock or pop concert after the main show, often held at a smaller venue for an invited audience.

adjective

  • Occurring after a performance; frequently in aftershow party.

Origin

Mid 19th century; earliest use found in Caroline Kirkland (1801–1864), writer.