Before long, you could have a large number of groups in your library. To help organize your groups, you can create up to 5,000 group sets. Group sets can contain any combination of custom groups and smart groups.
Use the plus (+) or minus (-) signs next to a group set header to expand or collapse the list of groups found in that group set. When the list is collapsed, the number next to the group set header reflects the total number of references found in each group. This number could include duplicates (references that are included in more than one group).
Some group sets are automatic and cannot be removed or renamed. These include Online Search and Find Full Text.
To get started with group sets, see: