Teams can be thought of as group initiatives in your organization. They may or may not be related to long-standing parts of your organization such as a department or division.
For example - you may have a one-time initiative to change your business model from a service based one to a product based model. This may cut across the current divisions of your organization and you may assign a team of people in your organization to work on all that it will take to make that transition in a current year.
Alternatively - you may have a team called Product Development or even assign a specific product to a team and that is where you would put the shared goals for that group.
Teams provide a flexible way for companies to have groups of people develop shared goals for a given initiative or area of the company.