What is the jutsu that ninjas use to appear/disappear instantly? Some users of the jutsu are Kakashi, Gai, Genma, Kabuto, etc. It can often be seen when Anbu members are dismissed.
The most common one I know of and I think you are talking about is the Body Flicker Technique (also known as Teleportation Jutsu, or Shunshin no Jutsu).




  The Body Flicker Technique is a high-speed movement technique,
  allowing a ninja to move short to long distances at an almost
  untraceable speed.*
  
  To an observer, it appears as if the user has
  teleported. A puff of smoke is occasionally used to disguise the
  user's movements. It is accomplished by using chakra to temporarily
  vitalise the body and move at extreme speeds. The amount of chakra
  required depends on the overall distance and elevation between the
  user and the intended destination.