"The Highest Possible Level of Development civilization. A gravely injured hermit comes to Trurl's house and tells Trurl of Klapaucius's adventure: Klapaucius wanders across an old robot, who tells him that he has logically deduced the existence of a civilization that reached the highest possible level of development (hence "HPLD"). He has inferred the existence of such a civilization by figuring that if there are different stages of development, there will be one that is the highest. He was then faced with a problem of identifying that one; as he noted, everyone claimed that theirs was the HPLD. Upon much research and thought, he decided that the only way to find it is by looking for a "wonder", i.e. something that has no rational explanation. Eventually Klapaucius discovers one such wonder: a star in the shape of a cube, orbited by a planet also shaped like a cube with the huge letters HPLD written on it."
Now I know how it is like, to be one of HPLD.