In a collection there may be items that relate to each other which are represented by the Related Items icon.
If an item has other related items associated with it, the icon will display below the thumbnail labels with the number of items it relates to in parentheses. The icon also displays in the top right of the Detail View. To view all related items, click on the Related Items icon to see them in the thumbnail view.
Related Items are enabled by editing the collection properties in the LUNA Collection Manager.