A more thorough explanation:

Definition: Federal tax law refers to all the rules and regulations that govern the collection of taxes by the federal government of the United States. This includes laws passed by Congress, court decisions, and guidance issued by the Internal Revenue Service (IRS).

Examples of guidance issued by the IRS include:

• Revenue Ruling: A public statement by the IRS that interprets and applies tax laws to specific situations.
• Revenue Procedure: A statement that provides guidance on how to comply with tax laws and regulations.
• Private Letter Ruling: A written statement issued to a taxpayer in response to a specific request for guidance on a tax issue.
• Technical Advice Memorandum: A written statement issued by the IRS to its employees that provides guidance on how to apply tax laws to specific situations.
• Field Service Advice Memorandum: A written statement issued by the IRS to its employees that provides guidance on how to apply tax laws to specific situations.
• General Counsel Memorandum: A written statement issued by the IRS's Office of Chief Counsel that provides guidance on how to apply tax laws to specific situations.
• Chief Counsel Advice: A written statement issued by the IRS's Office of Chief Counsel that provides guidance on how to apply tax laws to specific situations.

For example, if a taxpayer wants to know how to report income from a rental property on their tax return, they can look to IRS guidance such as a revenue ruling or revenue procedure for instructions on how to do so.