Facet refers to a small flat or shallow bony articular surface such as the articular facet of a vertebra.
In psychology, a facet is a specific aspect or characteristic of a trait or behavior. Facets can help to provide a more detailed or nuanced understanding of a trait or behavior, by breaking it down into smaller, more specific components.
For example, the trait of "extraversion" might be broken down into several facets, such as sociability, assertiveness, and talkativeness. Each of these facets represents a different aspect of extraversion and can vary independently of the other facets. A person might be high in sociability but low in assertiveness, for example, or high in talkativeness but low in sociability.
In psychology, facets can be useful for measuring and studying traits or behaviors because they allow for a more fine-grained analysis of individual differences. For example, a researcher might use a personality assessment that includes multiple facets of extraversion in order to get a more detailed picture of a person's social and interpersonal style.