Chiburi
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The chiburi, or blade cleaning, is part of the re-sheathing ritual known as "noto" practiced by the Japanese. The idea is that the dripping blood need to be cleaned from the blade before it is returned to the scabbard (saya). However, this act is mainly symbollic because a tap on the handle or sweeping the blade in an arc would not remove all the blood.
In an actual fight, it would be much more practical to wipe the blade as clean as possible on your (or your opponents) clothes, and then carefully clean it if you had more time. Blood is highly corrosive to steel, and nobody would risk leaving any on a valuable blade before sheathing it.
