An “Elfje” (little eleven) is a form of a short poem with exactly 11 words.
When written the poem has got 1 word on the first line, 2 words on the second line, etc. The fifth line has got 1 word online. It’s even better when you build tension in the poem over the first four lines and relieve that tension in the last line.
In print it should look something like this.
Four Five Six
Seven Eight Nine Ten