A monostich is a poem which consists of a single line.

The following is an example:

'Skunks,' the squirrel said, 'are sent to try us.'

Ralph Hodgson

Ralph Hodgson

Ralph Hodgson , Order of the Rising Sun ,was an English poet, very popular in his lifetime on the strength of a small number of anthology pieces, such as The Bull. He was one of the more 'pastoral' of the Georgian poets...

A monostich could be also titled; due to the brevity of the form, the title is invariably as important a part of the poem as the verse itself:

COWARD

Bravery runs in my family.

A. R. Ammons

Some examples of one-line poems were created by Ancient authors (Martial

Martial

Marcus Valerius Martialis , was a Latin poet from Hispania best known for his twelve books of Epigrams, published in Rome between AD 86 and 103, during the reigns of the emperors Domitian, Nerva and Trajan...

 e.g.). Modern monostich was started in Russia in 1894 when Valery Bryusov

Valery Bryusov

Valery Yakovlevich Bryusov was a Russian poet, prose writer, dramatist, translator, critic and historian. He was one of the principal members of the Russian Symbolist movement.-Biography:...

 published the single line of pretty absurdic essence:

О закрой свои бледные ноги.

In Western poetry monostich was reinvented by Guillaume Apollinaire

Guillaume Apollinaire

Wilhelm Albert Włodzimierz Apolinary Kostrowicki, known as Guillaume Apollinaire was a French poet, playwright, short story writer, novelist, and art critic born in Italy to a Polish mother....

in his "Chantre" (1914).