Yes, punch in means to record over top of a short section of a track. If the singer makes a mistake or an off note, punch in allows you to layer a new bit on top without re-recording the entire track. If your recorder or DAW software has this feature built in, it behaves like an automatic on/off switch for recording only from the starting and ending points that you select. Then during playback, the new "punched in" part plays at that area instead of the underlying mistake, (...and hopefully it sounds seamless.)