Seam allowance refers to the extra fabric that is left around the edges of a pattern when cutting out the pieces. It allows for sewing seams and provides some space for adjustments and finishing touches to the garment. Full definition
I don't allow for seam allowances in a pillow cover because I want my pillow form to fill the cover. (throughmyfrontporch.com)
To cover a pillow using the least amount of fabric possible, measure the pillow from seam to seam in each direction, then add a 1 - inch seam allowance on each side. (blowingawayoutwest.com)
Cut pieces of fabric to fit the openings of your console, including seam allowances on all sides and enough fabric for a rod pocket. (bhg.com)