Ball joint rubber boot, also a tie rod boot for some models, see below.

Fitments
Beetle lower ball joint boot for torsion bar models 1966 to 1979.
T25 Tie rod end boot
Golf Mk1 Tie rod end boot
Scirocco Tie rod end boot

Dust boots serve a simple but important purpose and allow joints exposed to the elements to stay clean and enjoy a long service life. If you notice or suspect that, dust boot is damaged / split replace it sooner than later to avoid expensive repairs.