A Lust Object is basically any item, idea, or generally person (they tend to be persons) that invokes a great rush of hormonal WANT in a subject.
This is the cause of many a SueFic, SIFic, AUFic, and the killing\bashing of the Lust Object's Love Interest when one exists. If such a case occurs where a luster discovers his or her Lust Object in near proximity, the encounter can result in glomping, squeeing, or the sudden stampeding to get near to said Lust Object.
Causing a canon character to display uncanonical symptoms of Nerdy Friend Crush Disease, whether the crush is focused on a canonical lust object or not, is a charge.
The Wanting of their Lust Object can occasionally cause problems for a PPC Agent assigned to a fic where that Lust Object is abused, or in some cases, just in near proximity. Agents' Lust Objects have been recorded by the Department of Personnel since an unfortunate incident in which an Assassin was cut down by phaser fire while lunging at a Mary Sue.