abdication
The act of a ruler giving up the throne.
Abdication is the act of formally giving up a position of supreme power, especially a throne. When a king or queen abdicates, they voluntarily step down from ruling their country, usually passing the crown to the next person in line.
The most famous abdication in modern British history happened in 1936, when King Edward VIII abdicated so he could marry an American woman named Wallis Simpson. The rules at the time wouldn't allow him to remain king and marry her, so he chose love over the throne. His younger brother became King George VI (the father of Queen Elizabeth II).
Abdication is different from being overthrown or voted out of office. A president who loses an election hasn't abdicated: they simply served their term and lost. But when someone with permanent power, like a monarch, chooses to give it up voluntarily, that's abdication.