Killing Intent

is simply the user exuding pure killing intention, and having it affect their opponent, themselves, and others around them, up to the point of paralysing them with fear. When the killing intent is particularly strong, it can even give the victim visions of their own gruesome death. This can cause killing intent to be confused with a genjutsu, despite it not being a technique at all. Striking the opponent with fear, it can prevent the bodily and systematic nerve endings from working unless one were to harness pain by injuring themselves to a high degree of pain to reverse the effect.

Trivia

 * can also be translated to "thirst for blood".
 * In Naruto the Movie: Blood Prison, Satori is capable of reading killing intent of its opponents, allowing it to instinctively dodge such attacks.