A wakizashi is a Japanese sword, longer than a tanto and shorter than a katana. They have a blade length of 18 inches, on average. It's also known as a kodachi. In the early 1600's, when Miyamoto Musashi popularized carrying and weilding two swords at once, samurai began pairing their katana with a wakizashi rather than a tanto, since a wakizashi is much more effective in combat. The custom of wearing a wakizashi along side a katana (called daisho) continued for centuries until carrying weapons in public was made illegal.