age-gap marriage; May-December marriage
Colloquial term for a marriage where the partners have a large age difference. Often used in media and everyday conversation.
See also: 年の差 (としのさ)
It seems age-gap marriages have been increasing lately.
She had a May-December marriage with a man 20 years older.
Compound of 年 (toshi, 'age'), の (no, possessive particle), 差 (sa, 'difference'), and 婚 (kon, 'marriage'). A relatively modern coinage reflecting social trends.