history
The phrase echoes the 《左传·隐公元年》 line 其乐也融融 ('how joyous indeed!'), describing the reunion of Duke Zhuang of Zheng and his mother after years of estrangement. The reduplication 融融 reinforces a warm, glowing happiness.
usage
Almost always describes group settings: families, reunions, classrooms, holiday gatherings. Use it to set scene rather than describe one person.
