The Constitution of Naboo was the planetary constitution of Naboo. In 24 BBY, the Royal House attempted to rewrite it so Queen Amidala could stay in office longer. She stepped down, anyway, with all the rights to retire from politics. This information seems to have been common knowledge, as Anakin Skywalker mentioned it to Amidala in 22 BBY.
The constitution had a provision that would allow the monarchy to once more become hereditary if a worthy dynasty could be found.