To distribute two channels of a stereo clip between the left and right channels. 

Mixers inside the DAW have a pan control knob for both stereo and mono channels. The pan operation for mono channels is the same for all DAWs and mixers: If you tilt the pan to the left, the sound will come from the left speaker, if you tilt it to the right, the sound will come from the right speaker. Of course, you don't have to tilt all the way to the left or all the way to the right.

For example, you can also position the volume somewhere between the exact right and the midpoint and in this way you can find the ''balance''.

The situation is slightly different for stereo channels. The pan control is used to adjust the "true" stereo pan on some DAWs, and to adjust the stereo balance in other DAWs.