library
In iMovie, the collection of video clips, photos, and other media that you import and the projects you create with them. Your project media is organized within events.
To view the contents of the library or an event within the library, select it in the Libraries list.
In most cases you have only one library, but you can add other libraries if you choose (for example, if you want to create an archive of your projects and events on an external storage device).