Button hole: a bound slit in a flap used to push a button through to close the flap. Buttonholes can be bound with fabric, but are most often bound with thread. Buttonholes can be parallel (vertical) or perpendicular (horizontal) to the direction of the flap. Buttonholes are parallel in places where there is not a lot of tug or pull. ie: down the front of a dress shirt of the length of a dress of skirt. Buttonholes are perpendicular in places that will have more tug or pull. ie: collars, cuffs, waistbands and on most children's-wear.
To make a buttonhole:
1. Measure the width and height of the button. This is how long you want the buttonhole to be.
2. Put in buttonhole presser foot and set machine to buttonhole stitch (if using a machine with an automatic buttonhole maker).
3. Practice a buttonhole on a scrap piece of fabric folded into three layers (this imitates the flap). Use the length measured and mark on buttonhole presser foot.
4. Adjust tension and length as needed and try again.
5. Sew the buttonholes!