I think it means that the singer is not singing live but is lip syncing instead (is a technical term for matching lip movements with sung or spoken vocals) Kindly see this link: https://www.google.com/#hl=en&tbo=d&output=search&sclient=psy-ab&q=mime+row&oq=mime+row&gs_l=hp.3..0l4.1384.2525.0.2801.8.8.0.0.0.0.602.1185.5-2.2.0.les%3Beqn%2Ccconf%3D1-2%2Cmin_length%3D2%2Crate_low%3D0-035%2Crate_high%3D0-035%2Csecond_pass%3Dfalse%2Cnum_suggestions%3D2%2Cignore_bad_origquery%3Dtrue%2Conetoken%3Dfalse..0.0...1c.1.Jo517Q6Dwp4&pbx=1&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bvm=bv.41524429,d.d2k&fp=2133deba519e1bd2&biw=1366&bih=643