Tabi (足袋) is a term for traditional socks unique to Japan, which is indispensable for Kimono (着物) style. Dating back to the Nara period, socks like we wear today was introduced from China, and was developed into Tabi shape later. Generally, white tabi is widely used, and in contrast, patterned ones for casual occasion are gaining popularity nowadays. Kyogenshi (狂言師, Noh commedians) wear yellow ones.
The major difference between socks and Tabi is that Tabi has its first and other toes separated (I know five toes socks are on market nowadays though...) People from overseas and/or youngsters who has no experience of wearing Kimono sometimes find it difficult to wear Tabi. However, you'd better to get used to it, because separating toes are very good for your health.
Geiko (芸妓) and Maiko (舞妓) usually have custom made tabi with their name engraved on Kohaze (こはぜ, metallic clasp). Everybody has different shape of feet, and perfectly fitted Tabi is very comfortable and makes your movement even more graceful.
Click here to see a Blog by a Former Maiko, "Do You Know?"