Snakeskin, like its name suggests, is literally the skin and scales of snakes (typically cobras, pythons, and Karung) which is treated and turned into clothing.
The snakeskin used in clothing is not the thin outer layer of skin shed by snakes naturally during molting, but involves actually killing the snake and skinning it, which has placed snakeskin under the scrutiny of PETA and other animal rights organizations. Manufacturers have also developed fake-snakeskin which looks pretty similar to the real thing, but does not involve the harming of animals.
Snakeskin used in large quantities is usually considered tacky and tasteless, but snakeskin used in small quantities can be considered edgy and exotic.

Snakeskin sneakers from Reebok

A serpentine snakeskin belt

A snakeskin cowboy boot

A bold and edgy snakeskin watch