Ballad and Common Meter (alternative iambic tetrameter and iambic trimeter)
This one's a classic, so it's no wonder it uses some of the most classic forms in all of poetry and music. "A Red, Red Rose" is written partly in ballad meter (the first eight lines) and partly in common meter (the last eight lines).
You know what that means—it's time for a little poetry lesson. Don't worry, we'll be brief, and then we'll get back to the poem at hand.
A poem in ballad meter consists of four-line stanzas (called quatrains) that alternate between iambic tetrameter and iambic trimeter. And in ballad meter, the second and fourth line of each stanza must rhyme (but the first and third do not have to). The only difference between ballad meter and common meter is that in common meter the first and third lines of each stanza, in addition to the second and fourth, must rhyme.