An organized offender is a criminal that carefully plans his crimes; choosing victims, bringing along items needed for committing said crime and a get-a-away strategy after the fact. This is seen in kidnappers, burglars and some rapists and murderers. It is the opposite of a disorganized or opportunistic offender who commits crimes without a plan.
An example of this is Ted Bundy, who, at least at first, carefully planned strategies for luring his victims, killing them and leaving their bodies in remote places. This is the way that he continued his rape/killing spree for several years before he was caught.