Contact groups in Google Contacts are simply lists of email addresses that let users quickly enter multiple addresses at once in their email messages, meeting invitations, and so on. Although groups that users create using Groups for Business are also lists of email addresses, they have their own group email address, so anyone with permission can send messages to that address.
Also, users can share content—such as Google documents and sites—with group addresses. And, unlike contact groups, the Groups for Business service includes advanced features, such as saving messages in a conversation history and moderation controls.