1.A collection of individuals formed to achieve the same goal or to participate in the same activity
2.Characterictics of the groups：
Interdependence、Common
Goal、Group
Personality、Commitment、Cohesiveness、Group
Conflict、Social
Facilitation、Gender Differences、Group
Size、Norms
3.Relevance、Relatedness、Timeliness、Sufficient
Length、Clarity、Informativeness、Openness
to evaluation、Provocativeness