The Uchigatana is a type of Japanese sword.

From the Heian to the Edo period, the primary battlefield sword was the tachi. Its long blade and sharp edge made it ideal for use on horseback. The Uchigatana was created during the Muromachi Period and, unlike the tachi,
was worn edge-up in the belt. Since it is worn differently, the
engraved words on the sword are also opposite to the tachi, making the
words still upright instead of upside-down like when one wears the tachi
like an uchigatana. This sword was developed out of the ever-increasing
need for speed on the battlefield, where quickly unsheathing one’s
sword and cutting down the enemy was a matter of life or death. Its
rapid acceptance indicated that battlefield combat had grown in
intensity. Since it was shorter, it could be used in more confined
quarters, such as inside a building.

Unlike the tachi, with which the acts of drawing and striking with
the sword were two separate actions, unsheathing the uchigatana and
cutting the enemy down with it became one smooth, lightning-fast action
(this technique was called battojutsu
otherwise known as Battokiri). The curvature on the blade of the
uchigatana differs from the tachi in that the blade has curvature near
the sword’s point (sakizori), as opposed to curvature near the sword’s hilt (koshizori)
like the tachi. Because the sword is being drawn from below, the act of
unsheathing became the act of striking. For a soldier on horseback, the
sakizori curve of the uchigatana was essential in such a blade, since
it allows the sword to come out of the saya (sheath) at the most
convenient angle for executing an immediate cut.

The word uchigatana can be found in literary works as early as the Kamakura Period,
but during that time the uchigatana was used only by individuals of low
status and privates in the ranks. Most uchigatana made during the early
Kamakura Period were not of the highest standard, and because they were
considered disposable, virtually no examples from these early times
exist today. It wasn’t until the Muromachi Period (considered by some to
be a kind of Dark Age in the history of the Japanese Sword), when the samurai
began to use them to supplement the longer tachi, that uchigatana of
high quality began to be made. In the Momoyama and Edo Periods, the
tachi was almost totally abandoned and the custom of wearing a pair of
long and short uchigatana together, the daisho (literally “big-little”), became the dominant sign of the Samurai class.  (Source: Wikipedia – http://en.wikipedia.org/wiki/Uchigatana)