A remixer is the person — often a DJ or a music producer — who takes a finished recording and makes a new version of it, adding to or changing the original so the song feels different in the club, on the radio, or online. The -er on the end marks the doer, the same way a baker bakes. People also use remixer for software or tools that help you remix, though the first meaning is a human. You will see it in music credits more than in everyday school talk. Though actually, the new song itself is not a remixer; that new version is a remix. The remixer is who made it.