Everyone is in high spirits and harmony during the festival.
Tips
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.