A grook ("gruk" in Danish) is a form of short aphoristic poem or rhyming aphorism, created by the Danish poet, designer, inventor and scientist Piet Hein, who wrote over 7000 of them, mostly in Danish or English. They have been published in 20 volumes. Some say that the name is short for "GRin & sUK" ("laugh & sigh" in Danish), but Piet Hein said he felt that the word had come out of thin air. The contemporary "Hunden Grog" (Grog the Dog) stories by fellow cartoonist Storm P. has, in public opinion, been regarded as an inspiration.
Piet Hein's gruks first started to appear in the daily newspaper "Politiken" shortly after the Nazi Occupation in April 1940 under the signature Kumbel Kumbell. The poems were meant as a spirit-building, yet slightly coded form of passive resistance. The grooks are multi-faceted and characterized by irony, paradox, brevity, precise use of language, rhythm and rhyme, and an often satiric nature.