Under the Internal Revenue Code, there are advantages for a Section 501(c)(3) organization to be classified as a "publicly supported" organization. To be "publicly supported," that organization must meet certain mathematical tests demonstrating a broad base of donor support (as compared to a small non-public pool of donors, such as a single family).
Previously, organizations that expect to meet the public support test would file a Form 1023 exemption application and seek a five year advance ruling. With such a ruling, the organization would generally be treated as publicly supported for its first five years. Then, it would need to submit a Form 8734 to show that its fundraising meets the publicly supported requirements, and if it did, the IRS would issue a final ruling establishing publicly supported status (or if it did not meet that status, it would be reclassified as a private foundation).
The IRS has now withdrawn the need to file a Form 8734 after 5 years. Instead, the taxpayer makes its own determination after 5 years, and if it meets the publicly supported requirements (and for so long as it does), it will report as a public charity without the need for a final determination by the IRS. The IRS will police the fulfillment of the public support requirement by new disclosures required on the Form 990 filings of the entity (assuming such a filing is required).
Note that if a public charity does not meet the public charity support requirements for two continuous years, it will lose its public charity status.
The IRS has issued a FAQ in question and answer format that address various transitional rules and other issues relating to the new reporting method.