This post is part of a series on understanding the meaning behind the values contained in a Two Line Element set, or Keplerian Elements. The main article is here.
International Designator (Piece)
This is a 3 letter code to designate the individual pieces from a successful launch.
The first code is A, the 26th is Z, the 27th is AA and so forth.
It is quite common to things such as A as a rocket body, B as a nose cone, C as a booster stage and D as one of the actual satellites.
The use of the first 5 digits of the international designator will let you search for all pieces from a particular launch.
99025DJM - FENGYUN 1C DEB (This satellite was destroyed by a Chinese Missile) The DJM denotes this as the 2977th piece (of the 25th launch in 1999)