Groups, channels, boards (or any other name you wish) -- the sub-communities enable you to create a focused space for members with shared interests or goals.
Here are some of the key elements of Groups:
Support free flow of discussions, questions, ideas, and knowledge with different content-types
Drive high-quality community contributions with reputation scores, badges, and leaderboard
Build the community with your branding to deliver a white-label experience
Categorize content and enable seamless knowledge discovery