Synchronicity
The Library module gives you access to all of the images that you’ve imported into the Lightroom catalog database. Yet, at times you may find it necessary to add or delete images from image folders outside Lightroom. In this case, these images haven’t been added or deleted from the catalog database and are thus inaccessible by Lightroom. To remedy this situation, go to the Folders panel in the Library module, Control-click (PC: right-click) on the image folder, and choose Synchronize Folder.