A more thorough explanation:

Treasury regulations

Treasury regulations are rules that explain how to apply the Internal Revenue Code. They are written in a book called the Code of Federal Regulations. The United States Department of the Treasury usually creates these regulations.

One example of a Treasury regulation is the rule that says you can deduct charitable donations from your taxes. Another example is the rule that explains how to calculate your income tax based on your earnings.

These examples show how Treasury regulations help people understand how to follow the tax laws. Without these rules, it would be hard to know how to calculate your taxes or what deductions you can take.