GMC

GMC stands for Goal, Motivation, and Conflict. This term was popularized by Deb Dixon, who does workshops and published a book on this topic.

Basically, the theory is this: All primary or secondary characters worthy of appearing in your story should have GMC, which can change over the course of the story and which can be expressed as follows:

[Character] wants [Goal] because [Motivation], but [conflict].

This is also one way to set up your story pitch when querying editors and agents.

EX: Susie wants to marry Johnny because she just found out she's pregnant with his baby, but she's engaged to Johnny's scary biker brother and the wedding's tomorrow morning.