A looper is a type of guitar pedal that records your guitar as you play and then plays that part back over as many times as you like in a continuous loop. You can then add to this loop by ‘overdubbing’ – playing a second part which will be recorded and added to the loop next time it circles round. It's an invaluable tool for any guitarist, whatever style of music you play as it has several really helpful functions for practice, writing music, recording and sampling, and live performance.
Ed Sheeran is the most high-profile guitarist who uses a looper pedal and uses a highly expansive looper prominently in his live shows to build out songs from scratch. Radiohead's Ed O'Brien, legendary virtuoso Paul Gilbert and Mastodon’s Bill Kelliher all use looper pedals in creative ways to enhance their music.