The Goodyear welted stitch is binding the last (or insole), the upper and the welt.
This stitch is horizontal and invisible on the finished shoe. Its main purpose is to ensure shoe solidity and flexibility.
These are two kinds of Goodyear welted shoes:
Goodyear-welted shoes that are glued
The welt is glued to the sole, there is no additional welt to strengthen the pair of shoes.
Goodyear-welted shoes with channel stitching
Sometimes Goodyear welted shoes may be manufacture using an additional welt : «the channel stitching». The sole is sewn to the welt with a small vertical stitch and it remains invisible. The real advantage of this technic is that it is possible for a cobbler to take out the sole to resole your favorite pair of shoes.