The name haiku is coined by the Japanese poet Shiki (Masaoka Shiki, 1867–1902).
The designation is based on the words hokku (ku) and hai. Hokku was the introductory verse in a collaborative poem, so-called renga, which some poets devoted themselves to in the late 19th century. Shiki came to call it ”ku”.
”Hai” can stand for a variety of concepts, but in the context of poetry it often stands for ”simple”.
Haiku is thus roughly equal to: simple verse.
ex:
April spring
summer is coming
in the plant pot
but … it cannot be that simple, can it?