Groups are a collection of nodes (nodes can belong to any number of groups).
The group alert status is determined by the worst status of any member node (which is in turn determined by the worst status of any node tests).
In this way the collective alert status of a group can be seen in the live monitor and main page.
Groups can be added, deleted, edited and reordered (the order in which they appear in the main list and any displays) through the Configuration - Groups option.
Selecting to edit a group allows you to set a name, description and icon (used in some displays) as well as add/remove member nodes.