What's a "Hang 10" ?

Hang 10 in chronological order:
1. Surfing stunt where the rider hangs ten toes over the nose of the board while continuing to ride.
2. Casual clothing line/manufacturer that featured a a bare foot print as its logo, usually appearing over the left breast on their knit shirts.
3. Optional package on '73 & '74 Dart Sports. Main features were the rear seat pass-through, sun roof, and unique decor. Supposedly the seat inserts were made from swim suit material.