Learner's definition of FOLLY
1 a : the lack of good sense or judgment : foolishness
b : a foolish act or idea : foolish behavior
the folly of driving fast on steep, winding roads
his folly in thinking that he would not be noticed
The folly of such an action should be apparent to everyone.
2 [count] : a very unusual or fancy building that was built in a garden for decoration or amusement in the past 3 follies [plural], chiefly US : a large public show or entertainment with many performers