Answer: Trait approach
Step-by-step explanation:
Trait approach is the technique that is used for studying and evaluating about the personality of an individual based on the traits displayed by him/her. Behavioral pattern, habits, emotions, feelings, views etc are assessed in form of trait markers for determining the personality of particular person.
According to the question, if personality of the friend is described as reserved, cheerful and friendly by a person then personality traits are being mentioned .Thus, the approach used for defining friend's personality is trait approach.