Pop art refers to a mid-20th-century art movement that originated in the United States and United Kingdom as a response to societal trends in mass culture, mass production, consumerism, and popular culture. The movement evolved to challenge existing fine art traditions on what art imagery could include and look like. Popular mediums of the Pop art movement included screen printing, painting, collage, assemblage, design, and illustration, which incorporated images from advertising, media, and celebrity culture.