Team work means working together to achieve a goal.
The term has it origins in the ancient word meaning family. The first teams were families, small groups of people dependant upon one another for survival. This style of working as opposed to individuals working alone was a recipe for success and has grown and become much studied with modern organisations adopting it in a variety of forms.
It is now a generic term and depending upon how it is used promotes the achievement of the goal or hinders it.
The most common use of the expression that I come across is groups of people who have the opinion that they are working well as a team. By that they typically meaning that they are cooperating and supporting one another.