Masaoka Shiki first used “haiku” in its modern sense in 1892.
Shiki’s innovation was not the invention of short Japanese poetry itself, but the creation and promotion of a new name for the standalone opening verse traditionally called hokku. Hokku had originated as the first stanza of linked poetry such as renga and haikai no renga, but by the late 19th century it was increasingly being appreciated as an independent poem.
In 1892, Shiki published a serialized work commonly translated as “Talks on Haiku from the Otter’s Den,” arguing for reform of the genre. He later promoted realistic observation, often described by the term shasei, or “sketching from life.” His advocacy helped establish haiku as a modern literary form rather than merely a fragment of collaborative verse.
A historical nuance is that the word haiku may have appeared earlier in a broader sense related to haikai verse. Shiki’s importance lies in making it the standard term for independent hokku, which is why 1892 is the conventional answer. He died in 1902 after a short but highly influential career.