Poetical writing created under some constraint, usually beyond the standard forms of constraint such as meter or rhyme -- perhaps a rule that words must be in a particular order (alphabetical, say) or form a structure in some way.
The more restrictive the constraint and the more artful the verse while being constrained, the better.
The day after writing the above, I serendipitously dusted off my copy of Le Ton beau de Marot and rediscovered it to be exercises in, and a book about, constrained verse, primarily poetry and prose.
Hofstadter revels -- nay, basks -- in constraint. Consider this passage from the introduction, page xix, describing some of the constraints involved (Hofstadter has just explained that he had complete control of the typesetting and composition of the book, as well as its content):
The amount of influence exerted on my text by concerns of purely visual esthetics is incalcuable -- and by "my text", I don't merely mean how I wound up phrasing my ideas, I mean the ideas themselves. Content has been determined by considerations of elegant form so often that I couldn't begin to imagine it. Every single line of text, for instance, is characterized by its spacing -- how wide the blanks between words are. I can clearly see the spacing as I type on my screen, and I rewrite and rewrite in order to make sure that no line is too tightly or too loosely spaced. In the course of such rewritings -- here extracting a word, there using a shorter or a longer one, elsewhere inserting a word where none was -- words and phrases that I would not have thought of pop to mind, suggesting ideas I would not have though of, and those ideas suggest unexpected paragraphs, and those paragraphs are in turn linked to other ones, and so on...
I know this sounds quite nutty, but it is me to the core. This is my style at its most pure, and, I must say, at its most joyous. Paradoxical though it surely sounds, I feel at my freest, my most exuberant, and my most creative when operating under a set of heavy self-imposed constraints. I suspect that the welcoming of constraints is, at bottom, the deepest secret of creativity -- and that, of course, is why poetry, built on a foundation of constraints -- and thus, needless to say, the merging of translation with poetry gives rise to such a rich mesh of interlocking constraints that the mind goes a bit berserk in a mixture of frustration and delight.
(Obviously, in the book this passage is beautifully typeset, as is the entire tome; sadly, I've not reproduced the composition here.)
As a whole, the book is quite artful within its constraints.