The eye and the pyramid shown on the reverse side of the one-dollar bill are in the Great Seal of the United States. The Great Seal was first used on the reverse of the one-dollar Federal Reserve note in 1935. The Department of State is the official keeper of the Seal. They believe that the most accurate explanation of a pyramid on the Great Seal is that it symbolizes strength and durability. The unfinished pyramid means that the United States will always grow, improve and build. In addition, the "All-Seeing Eye" located above the pyramid suggests the importance of divine guidance in favor of the American cause.
The inscription ANNUIT COEPTIS translates as "He (God) has favored our undertakings," and refers to the many instances of Divine Providence during our Government's formation. In addition, the inscription NOVUS ORDO SECLORUM translates as "A new order of the ages," and signifies a new American era. If you are interested in a more detailed history of the Great Seal of the United States, you should contact the Department of State directly.
Preceding text courtesy of U.S. Department of the Treasury.
Obverse: The eagle holds thirteen arrows in one talon and a laurel branch with thirteen leaves in the other. There are thirteen stars in the field surrounded by the wreath. The number thirteen refers to the thirteen original states which comprised the Union at the time of the American Revolution in 1776 and adoption of the U.S. Constitution in 1789. The motto on the banner in the eagle's beak is "E PLURIBUS UNUM", which translates as "One Out of Many."
Reverse: The pyramid likewise has 72 stones arranged in thirteen courses, including the base. The date in Roman characters at the base is 1776. The two Latin mottoes should probably read together, in which case the meaning is: "He approves the founding of a new order of the ages." The word SECLORUM does not mean "secular" but rather "of the ages".