May be you already know this. But still, read for just 2 minutes more to clarify your thoughts. Teams is an app which streamlines teamwork. That is the obvious definition. But this is an incomplete description.
Coordinating with multiple persons is Teamwork. Agreed. But there are a plethora of apps available to collaborate with others. What is special about Teams?
Teams is an app which helps you work with all types of Technologies. So it is not just teamwork with other people, it is with multiple technologies as well.