* A seven-line stanza within a larger poem, perhaps a free verse poem or a poem with a more unconventional structure.
* A free verse poem if it's a complete poem with no rhyme scheme or specific meter.
Ultimately, the lack of rhyme doesn't automatically give it a unique name. You could describe it as a "seven-line poem without rhyme" or "an unrhymed seven-line verse" to be clear about its form.