Answer

“Nonprofit” and “not-for-profit” are often used interchangeably.  For more info refer to this article.  In brief: 

A nonprofit is one that qualifies for tax-exempt status by the IRS because its mission and purpose are to further a social cause and provide a public benefit. Nonprofit organizations include hospitals, universities, national charities and foundations. 

A not-for-profit organization (NFPO) is one that does not earn profit for its owners. All money earned through pursuing business activities or through donations goes right back into running the organization. An example is a sports clubs. 

For resources available go to the NYU Business Library's Company & Financial Information section and search in the following suggested resources: 

GuideStar, the National Database for Nonprofit Organizations

Foundation Directory Online (A foundation is a legal category of a nonprofit organization)