The Five Factor Model is also often known as The Big Five. It focuses on five main personality traits and determines to what degree you have each of them. The five traits are extraversion, agreeableness, openness, conscientiousness, and neuroticism. The way it works is that it uses a continuum. The respondent will fall on a continuum for each trait, depending on the strength of that trait in their personality.
This is one of the most widely accepted personality theories today, perhaps because it uses a continuum method rather than categorizing and labelling people. It is often used during recruitment. Personality assessments can be useful tools for hiring managers looking for certain traits in the people they recruit.