Answer:
Psychology -- the scientific study of behavior and mental processes, contains many sub-fields -- such as comparative (animals v. humans); biological; psychotherapy or counseling; abnormal or psychopathology, and SOCIAL. Social psychology is the scientific study of behavior and mental processes that examines social interactions and how we humans think about other humans. This sub-field of Social Psychology might examine what tends to influence people, how we tend to react in social situation, how we form and express attitudes and beliefs about the world, how we attribute causes to phenomena, conformity, racism and so forth. etc.
Personality psychology is a separate area of investigation, but is more and more combined with Social Psychology. The focus of Personality in contrast to Social is on qualities we are born with or that form which are maintained over time and across situations. The psychology of Personality will tend to examine how we DIFFER from one another whereas Social Psych. will TEND to emphasize general laws of behavior or how HUMANS, on AVERAGE, react to various situations. These are different ways of viewing the world, but might be used to examine the same or similar phenomena: both are legitimate thus the combining of the two subfields.