Seam allowance
Seam allowance (sometimes called inlays) is the area between the edge and the stitching line on two (or more) pieces of material being stitched together. Seam allowances can range from 1⁄4 inch (6.4 mm) wide to as much as several inches. Commercial patterns for home sewers have seam allowances ranging from 1⁄4 to 5⁄8 inch (6.4 to 15.9 mm).
Sewing industry seam allowances range from 1⁄4 inch (6.4 mm) for curved areas (e.g. neck line, armscye) or hidden seams (e.g. facing seams), to 1 inch (25 mm) or more for areas that require extra fabric for final fitting to the wearer (e.g. center back).
...
Wikipedia