What is the name of the most commonly used tax return form?

The most commonly used tax return form in the United States is the IRS Form 1040. This form is utilized by individual taxpayers to report their income, claim deductions and credits, and calculate their tax liability. There are variations of this form, including the 1040-SR for seniors and the 1040-NR for non-resident aliens, but the standard Form 1040 is the most widely used.