Despite a lack of definition in Section 501(c)(3) of the Tax Code or the Regulations, the IRS and the courts have used the term “in its generally accepted legal sense”
An organization will not qualify for charitable exemption if it provides private benefit which is not quantitatively and qualitatively incidental to the public benefit of its activities.
Neither the Tax Code nor the Regulations provides a definition; The IRS uses a 14-point set of guidelines, plus the other limitations of Section 501(c)(3)