An ItemInfoValue is always associated with an Item. Its primary purpose in the public API is for developers of custom items.
The item's ItemInfoValue contains many of the item's details to include title, description, path, type id (read from the Config.daml), associated tags (if any), and so forth. In most cases, Pro constructs the ItemInfoValue for you using the values for your custom item component entry in the Config.daml. It is typically passed to its "containing" Item when the Item is constructed.

Reference

ItemInfoValue Members
ESRI.ArcGIS.ItemIndex Namespace