marital harmony; happy marriage
Describes a state where a married couple gets along well and the marriage is peaceful and happy. Often used in set phrases like 夫婦円満の秘訣 (the secret to a happy marriage).
The secret to a happy marriage is respecting each other.
That household always seems so harmonious; I'm envious.
円満 alone means 'harmony' or 'peacefulness' in a broader sense, while 夫婦円満 specifically refers to marital harmony.
Compound of 夫婦 (married couple) and 円満 (harmony, peacefulness).