.PHOTOSLIBRARY File Extension
File TypePhotos Library
What is a PHOTOSLIBRARY file?
Library of digitals photos created by Photos, an image organization application bundled with OS X 10.10.3 and later; contains data referenced by your Photos Library, which includes thumbnails, resources, albums, and other properties; located in the "Pictures" folder of your home directory.
NOTE: The PHOTOSLIBRARY package used by the Photos application is similar to the .PHOTOLIBRARY package used by iPhoto application, which Photos replaced in 2015.