A "high frequency blade" is generally used only in fiction, though it may exist in real life.
In the video game series "Metal Gear Solid", it is used in "The Twin Snakes", "Sons of Liberty", and "Guns of the Patriots" by the ninja characters and Raiden.
Essentially it is a Samurai sword-like blade (or "shinobi-gatana" or "ninja-to" to be more proper) that has a device in the handle that vibrates the blade at a high frequency (hence the "high frequency blade") enableing it to cut more easily and with less friction through harder substances.
The blade moving up and down very quickly and marginally makes it function as a sort of jigsaw to accentuate a normal human's cutting power. | 
