Stitch Compensation, also known as fractional stitches and partial stitches, refers to a section of a stitch made when the area to be stitched is too small to fill an area in its entirety, or when the boundaries of the stitch might extend into an unwanted area.
I've used a row of the Plaited Gobelin variation here as an example. With this stitch, compensation stitches (in light blue) were added to each end of a row to fill it out. If the compensation stitches were not there, the stitch would look unfinished at the ends of the row.
The blue border was worked from left to right, starting with the compensation stitches and then working the full stitch. The end of the border also features a set of compensation stitches to fill out the opposite end.