An Export Group is a container that is linked to any # of Export Assets to define how those Asset should be exported. For animation a Group can be considered an individual animation file and multiple groups can be defined to export multi-part animations from a single file.
Right Clicking an Group will bring up the Export Asset/Group Menu
Move the selected Group up or down in the Group List
Filter - Only display Groups that have names that contain the entered filter string.
Group List - List of all Export Groups in the scene.
Export Checkbox - Whether or not the Export Group should export when Export Assets is run.
Create Export Group - Create a new Export Group.