What unwritten custom did the 22ND amendment establish as law?

The 22nd Amendment to the U.S. Constitution, ratified in 1951, established the unwritten custom of limiting presidents to two terms in office as law. Prior to this amendment, the tradition of serving only two terms was largely followed since George Washington opted not to seek a third term. The amendment was enacted in response to Franklin D. Roosevelt's four-term presidency, aiming to prevent any future president from holding excessive power for an extended period.