Psychokinesis

Psychokinesis (念力 (サイコキネシス) ) (PK) in the Toaru Majutsu no Index universe is one of two criterias that esper powers are grouped into, the other being ESP or Extrasensory perception.

Basically, PK involves influence of an object external to the user. Powers that allows one to physically affect an object are classified in PK, like Telekinesis.

Principles
As explained by Tsukuyomi Komoe, PK has a higher precedence in classification of esper powers than ESP, especially when an esper power sits on both sides of the boundary between ESP and PK.