Answer by taking a quote from the following article:

The New York Public Library (NYPL) is a public library system in New York City. With nearly 53 million items and 92 locations, the New York Public Library is the second largest public library in the United States (behind the Library of Congress), and fourth largest in the world. It is a private, non-governmental, independently managed, nonprofit corporation operating with both private and public financing. The library has branches in the boroughs of Manhattan, The Bronx, and Staten Island, and affiliations with academic and professional libraries in the metropolitan area of New York State.

The Library website provides access to the library's catalogs, online collections and subscription databases. It also has information about the library's free events, exhibitions, computer classes and English as a Second Language (ESL) classes. The two online catalogs, LEO (which searches the circulating collections) and CATNYP (which searches the research collections) allow users to search the library's holdings of books, journals and other materials. The LEO system allows cardholders to request books from any branch and have them delivered to any branch.  The NYPL gives cardholders free access from home to thousands of current and historical magazines, newspapers, journals and reference books in subscription databases, including EBSCOhost, which contains full text of major magazines; full text of the New York Times (1995-present), Gale's Ready Reference Shelf which includes the Encyclopedia of Associations and periodical indexes, Books in Print; and Ulrich's Periodicals Directory. The New York Public Library also links to outside resources, such as the Bureau of Labor Statistics' Occupational Outlook Handbook, and the CIA's World Factbook. Databases are available for children, teenagers, and adults of all ages.  The NYPL Digital Collections (formerly named Digital Gallery) is a database of over 700,000 images digitized from the library's collections. The Digital Collections was named one of Time Magazine's 50 Coolest Websites of 2005 and Best Research Site of 2006 by an international panel of museum professionals.  The Photographers' Identities Catalog (PIC) is an experimental online service of the Photography Collection in the Stephen A. Schwarzman Building.  Other databases available only from within the library include Nature, IEEE and Wiley science journals, Wall Street Journal archives, and Factiva. Overall, the digital holdings for the Library consist of more than a petabyte of data as of 2015.

what are digital holding?
is a database of over 700,000 images digitized from the library's collections.