According to American psychologist Gordon Allport's Trait Theory (1937) the traits that make our personality unique, from one individual to another, should be classifiable and organized in a manner similar to the way that we graphically organize words in a dictionary. Some traits are stronger than others, and some are more salient. Those traits which are strongest and most salient are the ones that should correctly describe the personality of an individual, rather than awarding general traits to someone just for the sake of description. That is the intention of his theory.
Now, the structure and dynamics as defined by Trait theory are based on three categories of traits that all individuals possess: the Cardinal trait, the central trait, and the secondary trait.
The cardinal trait is your most salient and powerful trait. It molds your choice making processes and behaviors. They also drive the internal motivation of the individual. This is how you get your compulsive types, the shy types, the impassioned types, the Type-A people, etc. You know that the trait is cardinal if it affects the overall behavior and demeanor of the individual.
The central trait are universal traits that most everyone possesses, at VARYING degrees, but are still there. For example, all individuals at one point or another are shy, or courteous, or moderately well-mannered, or honest, for the most part. Again, it is the general characteristics that we all have, though some may be more accentuated in ones than in others.
The secondary traits are the quirks. Those truly unique separators that make some people look strange because of their particularity. For example, someone who cannot tolerate dinginess and is extremely focused on specifics of cleaning has an obsessive trait that separates them from the rest. The same happens with the picky eaters, the "extremists" and other types of individuals with a truly salient trait that is hardly shared by many. Those reality TV shows featuring people who hoard, or that won't spend any money, or that develop fixations with objects are suffering from a secondary trait. The obsession cannot be classified as a cardinal trait unless it completely defines their behavior uniformly. In those cases, however, there is usually an intervention to break with the habit.