Primary groups are small, long-term groups characterized by intimate communication and high levels of cohesiveness that provide security. Secondary groups are larger with less intimacy and more goal-focused to achieve objectives. Temporary groups form for a particular purpose and end when the purpose is fulfilled, while permanent groups last a long time with strong bonds over similar interests. Formal groups have specific goals and boundaries to follow, lasting varying amounts of time, compared to informal groups that form flexibly as needs arise without structure.