When flying from A to B, the effect of the wind needs to be considered. If you were to simply point the aircraft’s nose towards B, the wind may blow you off track.
To fly along the desired track, we need to change the heading of the aircraft to be slightly into wind.
Drift is the angle between the aircraft’s heading and the track made good (i.e. how far the wind is pushing you).
When the difference between our heading and desired track equals the drift, our track made good will match our desired track.