We can explore those questions from different angles, but my simplified definition is: a team is a group of individuals moved by a common goal. Everything is better if, in the meantime we move together towards the goal, we share a positive energy and attitude in between the group.
Retrospective meetings are recurring meetings that usually take place after the sprint review. These are very important moments to make a team think about what can be improved. But sometime there are moments when the team is faced with some difficulties in dealing with problems.