serial number - Boeing 747 | information center

Serial or construction number (common abbreviation s/n and c/n) or Manufacturer serial number (MSN)

example:

PH-CKA B-747-406ER/F 33694 / 1326 RL681 R7166

Number given to an airplane after a firm order. Often airlines or lessors order aircraft in serial numbers blocks. Not all serial numbers are actually built. It's also possible that a higher serial number is actually built earlier than a lower number (out of sequence).  A serial number identifies the aircraft but gives no additional info.