The term "Microform" is simply an extremely small form or item. In the context of libraries, we are referring to microfilm, microfiche, or microcards. By photographing an object, it can be reduced in size and stored in a smaller space. This also always libraries to preserve materials and prevent it from deteriorating.
All microform materials are accessible through OneSearch and can be requested using your library account. Simply log in using your CUNY credentials.
The University of California has provided an extensive history of microfilm: The History of Microfilm: 1839 To The Present
The Association for Library Collections and Technical Services provides best practices for managing micro-format collections: Managing Microforms in the Digital Age