OER textbooks: 

• are available at no cost to faculty and to students
• can be modified by faculty and/or students
• can be redistributed by faculty who have made changes to the original OER work

OpenStax, a nonprofit based at Rice University, has created a suite of peer-reviewed, open source textbooks, including Sociology 2e. You can find more information about it, and download it, here. 

For the Hunter College "Zero Cost" program, textbooks need only comply with the first feature, that they are available at no cost to faculty or students.

If you are Hunter faculty, already using a textbook, and wondering if it will fulfill the goals of the zero cost program, you can email me or Alexandra Gil, in the library.