Rumors have been studied for several decades in social and psychological fields, where most studies were theory-driven and relied on surveys due to difficulties in gathering data. Rumor research is now gaining new perspectives, because online social media enable researchers to examine closely various kinds of information dissemination on the Internet. In this paper, we review social psychology literature on rumors and try to identify the key differences in the dissemination of rumors and non-rumors. The insights from this study can shed light on improving automatic classification of rumors and better comprehending rumor theories in online social media.