Upholstery is the craft of restoring anything covered with fabric/leather. We often think of antique chairs, but auto interiors, motorcycle seats, gym equipment, medical equipment, decorative walls, speaker boxes . . . all are covered with some kind of material that ages and wears out. Restoration means making a seat look and feel like new by repairing the frame, the springs, and the cushioning – not just replacing the cover material.
Sometimes buying new makes more sense than restoration. Seats from a 1929 Ford Model A? Upholstery is your only choice. Thirty restaurant chairs? It may be smarter to buy new ones. Keep in mind though, poor quality chairs that break quickly are a waste of money. Restoring chairs with a good, solid frame will last longer and therefore save you money in the long run.