The name of “Japanese sword” is quite new and it started around the end of Tokugawa Shogun period when they started more business and cultural exchanges with foreign countries. Before that period, it was just called as “Katana(刀)” or “Tsurugi(剣)”. After Muromachi (室町)period (around A.D.1,500), the Japanese swords are classified into three different categories based on their length.
Uchikatana(打刀) over 60cm
Wakizashi(脇差) 30cm〜60cm
Tantou(短刀)less than 30〜36cm
In Muromachi period, they used their swords on horses in the battle and the sword was long with a large curve shape. It is called Tachi(太刀)and the length is about 75.8〜78.8cm long. When they carried Tachi putting on a sword with its edge down.
On the other hand, Uchikatana was put on between belts with its edge up.
Reference:「刀剣ワールド」