Gwawdodyn Byr is a Welsh meter based on quatrains that is nearly, but not quite, isosyllabic. It features two nine-syllable lines followed by two ten-syllable lines, with a single rhyme sound that appears on all four lines. The sound appears at the end of lines one, two, and four, but in the middle of line three.
The Gwawdodyn verse form is the 20th of the codified Welsh meters. This form is made up of quatrains comprised of distinct couplet forms that are, themselves, other members of the codified meters. More specifically, a Gwawdodyn verse will be a Cyhydedd Naw Ban couplet followed by either a Toddaid or a Cyhydedd Hir.
The toddaid is one of the 24 codified Welsh meters. This particular poem form consists of uneven couplets with lines of ten and nine syllables, featuring unusual rhyme schemes that utilize a technique called gair cyrch, ultimately resulting in staggered rhymes that feel exotic to English readers and writers.