Anbu

The is actually short for. The name is a form of contraction, similar to English acronyms like SWAT, where the two kanji used to abbreviate the group's full name constitute an actual word on their own.

Dress
The ANBU wear porcelain animal masks in order to distinguish themselves from normal shinobi and to conceal their identities. They also have standard uniforms consisting of black and gray armor, arm guards, and a signature spiral tattoo on their left shoulder. Certain ANBU wear black cowls over their standard uniforms, and squad leaders may wear white cowls.

Purpose
ANBU protect the village from exceptional threats, conduct high-risk missions into enemy countries, and deal with extremely strong ninja. They are also responsible for carrying out assassinations and missions requiring specially trained ninja. Unique for most characters in Naruto, all ANBU carry Ninjaken, which are usually strapped to their backs, and they all know the layout of the human body in detail. By using Temporary Paralysis Technique, ANBU members can paralyze an opponent, leaving them open for attack. With Time Reversal Technique, an ANBU can put someone in a state of reverse hypnosis, allowing them to remember details that they otherwise would not. They serve under the direct command of their Kage.

Known ANBU members

 * Kakashi Hatake (former Konoha ANBU captain)
 * Raidou (a squad captain that tried to save Third Hokage from Orochimaru. In the filler, he and his team interrogates Naruto about Gennou)
 * Zabuza Momochi (formerly assassination expert for Kirigakure)
 * Raiga Kurosuki (formerly ANBU member for Kirigakure)
 * Itachi Uchiha (former Konoha ANBU captain at the age of 13)
 * Ibiki Morino (head of the Konoha's ANBU Torture and Interrogation Squad)
 * Yamato (undercover as a Jonin)
 * Sai (member of Konoha's ANBU "Root")
 * Danzo (leader of Konoha's ANBU "Root")
 * Unknown ANBU (member of Konoha's ANBU "Root" seen talking to Sai before his first mission with Team 7)
 * Yugao Uzuki (girlfriend of Hayate Gekko)