Just a guess because I looked it up…
What Is Unrelated Business Taxable Income (UBTI)?
Unrelated Business Taxable Income (UBTI) is the income earned by a tax-exempt entity from activities that are not related to its exempt purpose. The Internal Revenue Service (IRS) defines UBTI as “income from a trade or business, regularly carried on, that is not substantially related to the charitable, educational, or other purpose that is the basis of the organization’s exemption.”