A more thorough explanation:

Term: REV. RUL.
Definition: Rev. Rul. is an abbreviation for Revenue Ruling. A Revenue Ruling is an official interpretation by the Internal Revenue Service (IRS) of the tax laws. It provides guidance on how to apply the tax laws to specific situations. Revenue Rulings are published in the Internal Revenue Bulletin and are binding on the IRS and taxpayers.
Example: An example of a Revenue Ruling is Rev. Rul. 2019-24, which provides guidance on the tax treatment of cryptocurrency hard forks. The ruling explains that if a taxpayer receives new cryptocurrency as a result of a hard fork, the taxpayer will not have taxable income until they sell or exchange the new cryptocurrency. This ruling helps taxpayers understand how to report their cryptocurrency transactions on their tax returns.
Explanation: The example illustrates how a Revenue Ruling provides guidance on how to apply the tax laws to a specific situation. In this case, the ruling explains how to report cryptocurrency transactions on a tax return. The ruling is binding on the IRS and taxpayers, so taxpayers can rely on it when preparing their tax returns.