Groupthink is a term coined by Irving Janis in 1972. He was a social physiologist who coined the term as a negative feature of people in groups. According to him, group pressures lead to deterioration of mental efficiency, reality testing, and moral judgment. This is a result of a collective failure to see alternatives and seek for better solutions. It's a result of going for a dehumanized and irrational option.
Groupthink causes them to shut off the outside influence and work as per their own following and groupthink. Although the term was coined as a negative one, groupthink now has both positive and negative versions. Groupthink is essentially a psychological phenomenon wherein a group of people is looking for common harmony and desire. If the purpose is positive and the end result is positive, it is called a positive groupthink while if the outcome is negative, it becomes negative groupthink.