Selvage
The tightly woven finished edge along both sides of a woven fabric, which keeps it from unraveling.
The selvage runs parallel to the lengthwise threads, so it is the reference for the grainline. It is often denser and can shrink differently from the rest of the fabric, so it is kept out of the pieces and the usable width of the fabric is measured between the selvages, discounting any edge that cannot be used.
Example
A fabric sold as 150 cm wide may have only 146 cm of usable width once the selvages are discounted; the marker is built to the usable width.