There are various classifications for nonprofits and charities that are designated by the Internal Revenue Service as having a tax exempt status. The most general EO (Exempt Organization) classification is a 501c corporation, but there are also 501(c)(6) organizations and 501(c)(3) charitable organizations. For more details, refer to this IRS link.
While non-profits and charitable organizations have tax exempt status, they are required by law to file a Form 990. Many websites allow you to search for these filings, including the National Center for Charitable Statistics at the Urban Institute (see below under Internet Resources )
When searching USC databases, use terms like: NONPROFITS, NOT-FOR-PROFITS, PHILANTHROPY, CORPORATE GIVING, CORPORATE RESPONSIBILITY, SOCIAL RESPONSIBILITY, SOCIAL CAUSES, FUND RAISING, CHARITIES, CHARITABLE FOUNDATIONS, DONATIONS, GRANTS, FOUNDATIONS, ENDOWMENTS. Use area of focus to refine results (e.g.: education, conservation, human rights, youth organizations). Search on specific entities such as the Bill & Melinda Gates Foundation.
When available, search NAICs code: