Panning audio means to direct a sound signal to a different part of the stereo field. This basically means panning controls how each track is balanced between right (R) and left (L) sides of where the audio is being heard from. So, if you move it all the way to the right, you can hear the audio for that track only on the right side of your headphones or speakers.
For example, if a child is laughing on the right side of a scene, panning the sound to the right creates a realistic experience for the viewer.