What does Goodyear welted mean?
The “welt” is a strip of leather which is sewn around the bottom edge of a shoe. This stitching attaches the welt to both the insole and the upper of the shoe. The welt is folded out to form a point of attachment for the outer sole. The outer sole (two layers can be used in heavier shoes) is sewn to the welt, with a heavy-duty lock-stitch seam.
Crucially, this stitching runs around the outside of the sole (rather than piercing the part under the foot) to maximise the sole’s water-resistance.