A group is a set of users that have a common position, goal, or concern.
You can create groups of people or use groups that are already created for your organization by your service administrator. You can add groups as a member to a conversation or a folder, or share an object with the group. This lets you share information with a large number of people at one time.
The great thing about using groups is that you can make sure no one is accidentally left out. And, if someone new needs to be included, you can add them to the group rather than tediously adding them to each object that they need to know about.