Groups are collections of two or more people who interact, share some common idea, goal, or purpose, & influence how their members think & behave.
Group cohesion a.k.a. group togetherness, is determined by how much group members perceive they share common attributes.
Group norms are defined by formal or informal rules about how group members should behave.
In a Task-oriented group members have a specific duties to complete.
In a Socially oriented group members are primarily concerned about fostering and maintaining social relationships among the members of the group.
Robert C. Gates