What is the term for willingly renouncing one's citizenship to reside in another country?

The term for willingly renouncing one's citizenship to reside in another country is expatriation. This process involves a voluntary decision to abandon one's citizenship in favor of living in a different nation, which can entail various legal and personal implications. Expatriation can result from a variety of reasons, including personal preference, career opportunities, or lifestyle changes.

Migration refers more broadly to the movement of people from one place to another, often without the implication of renouncing citizenship. Immigration specifically involves moving into a country with the intention of settling there, typically while retaining the original citizenship. Emigration describes the act of leaving one's resident country to live in another, but it does not necessarily involve renouncing citizenship. Thus, expatriation is the most accurate term for the situation described in the question.