Tabi socks, or split-toe socks, have been worn in Japan since the sixteenth century, reaching their peak popularity during the Edo period (1600-1868). They were developed to wear with sandals & wooden clogs called geta. Lots of people wear tabi socks: martial artists practicing Aikido or Karate, Taiko drummers, and traditional Japanese folk dancers, just to name a few!
Traditionally, tabi socks were plain and came in monochrome colors like black and white. These days, modern tabi socks are colorful and can have different designs on them. There are different styles, too, including the "five-fingered sock" that fits the toes like a glove. Both Japanese shops and online stores sell these trendy socks.