Building a team is critical to achieve the goals and objectives of any project, as most project managers will tell you. Unfortunately, few project managers build effective teams . Instead, they treat their project as a committee; members meet, do what they have been told, and depart. Synergy is lacking.
What is a team? One common definition is that a team is a group of people with each one having a narrow set of skills, knowledge, and interests that are applied to achieve a common purpose.  This definition, like many others, is incomplete. The team is viewed like a machine. The emotional and psychological aspects are missing.
The best definition is one that appears in The Wisdom of Teams by Jon Katzenbach and Douglas Smith where they define a team as a small group of individuals with complementary skills that are applied to achieve a common goal by which everyone is held accountable.  The operative words in this definition are complementary, common, committed, and accountable.
Complementary means that a team consists of people with different skills. Common means that people share a destination and path when applying their complementary skills. Committed means that they have a personal stake in activities and outcome. Accountable means that their participation contributes not only to their own success but also to that of others and the entire project.
Why does a team prove more valuable than individual efforts? It is the synergistic quality. According to Katzenbach and Smith, teams are the "basic unit of performance" that reflects the composition of many skills, experiences, and judgment. In other words, a team is more than a mere collection of people, e.g., committee. In addition, teams are more adaptable and productive than other organizational units because they often have clearer goals, which lead to better performance. 
 Karen Bemoski, What makes American teams tick?, Quality Progress , pp. 39 “40, January 1995.
 Jon R. Katzenbach and Douglas K. Smith, The Wisdom of Teams , Harvard Business School Press, Boston, 1993, p. 45.
 Jon R. Katzenbach and Douglas K. Smith, The Wisdom of Teams , Harvard Business School Press, Boston, 1993, p. 15.