You can perform various tasks with the items in a content library. You can synchronize an item from a subscribed library to download all its contents and use the item to deploy a virtual machine for example. You can delete items you no longer need to use, and so on.

Each template or other type of file in a content library is a library item. An item can contain a single file or multiple files. For example, when you add an OVF template to the library, you actually upload all the files that are associated with the template, but in the vSphere Client you only see one library item of the OVF Template type.