Nonce forms, typically, are given short shrift by standard poetry dictionaries and guidebooks. Lewis Turco provides a minimalist if admittedly conventional definition ("Many poems are 'regular,' that is, traditionally formal, but the specific combinations of stanza pattern, line length, rhyme schemes, and meters have sometimes been created by the poet for that specific poem"), but neither The New Princeton Encyclopedia of Poetry and Poetics, nor Abrams, Baldick, Kennedy, et al., have one.
Our definition of nonce forms may be considered by some too loose, by others too restrictive, and maybe that's for the better. So here goes: a nonce form is generally created by a poet for a specific poem but which may, over time, and with repeated usage by subsequent poets, become a "received form." We cast a broad net, from the more traditional sense of stichic and/or stanzaic patterns generated/"invented" for a specific poem, to a more liberal definition wherein we most verge towards "organic form" (as in Levertov's "Form is the revelation of content."; or Creeley's "Form is never more than the extension of content.") seeking some identifiable element of regularity, usually in relation to rhythm and sound, but possibly looking towards visual dynamics. Certainly sound and visuality can play off of each other in fascinating ways. All poetry has form, which is why we don't say we're a journal of "formal poetry." We're happy to entertain a wide range of nonce forms, from variants of metered stanzas (such as the heterometric stanzas of Herbert and Keats, among others) to the "Fib" (syllable counts based on the Fibonacci sequence, invented by Gregory K. Pincus, e.g. A. E. Stallings's sequence in The Cortland Review), and almost innumerable others. Ultimately, we concur with David Barber in hoping that nonce form poems we receive will "kindle a spark of that original sense of discovery and immediacy in a way that won't seem dutiful or mechanical." In other words, try us.