Final answer:
One term of office for the U.S. President is four years, with the 22nd Amendment limiting a president to a maximum of two terms, or a total of ten years under specific circumstances.
Step-by-step explanation:
One term of office for the U.S. President is four years. Initially, the U.S. Constitution did not limit the number of terms a president could serve. However, after President Franklin Delano Roosevelt was elected to four terms, the 22nd Amendment was ratified in 1951, which established that no person could be elected to the presidency more than twice, thereby limiting a president to a maximum of two terms in office. The exception is if a vice president steps into the presidency and serves two years or less, they can run for two full terms, meaning they could potentially serve for a total of ten years.