Feast of Fools was a festival that happened a long, long time ago in some parts of Europe. It was celebrated at the beginning of January, usually on the day of Epiphany. During this festival, people would dress up in funny and crazy costumes and play tricks on each other.
It was sort of like Halloween, but instead of scaring people, they would make them laugh. People acted silly and danced around, and everyone had a lot of fun.
The Feast of Fools started as a way to kind of turn the tables on the church. The church was very serious and strict, and people wanted a chance to let loose and have fun. So, for a short time, they would act like the church officials, but do it in a silly way. They would put on fake religious ceremonies, and people would act like they were priests and nuns.
The Feast of Fools was eventually banned by the church because it was seen as too disrespectful. But it was still remembered as a time when people could let go of their normal roles and be silly and fun for a while.