What is the name for that portion of the U.S. Constitution that explains the purposes of the United States government?

The portion of the U.S. Constitution that outlines the purposes of the government is known as the Preamble. It serves as an introduction to the Constitution and articulates the foundational goals, such as promoting justice, ensuring domestic tranquility, and securing the blessings of liberty. The Preamble sets the tone for the articles that follow and reflects the intentions of the framers.