Strictly, a ballad is a form of poetry that alternates lines of four and three beats, often in quatrains, rhymed abab, and often telling a story - the anonymous poem 'Sir Patrick Spens' and Wordsworth's "A Slumber Did My Spirit Seal" demonstrate this well. The alternating sequence of four and three stresses is sometimes called common measure, especially when used for hymns. It is an appropriate name, as it is a very common form, with examples found from medieval lyrics to contemporary birthday cards, and is often the form used on TV when the scriptwriters want a character to have written a poem.
Within the Archive, Brian Patten's use of the form in 'Geography Lesson' echoes John Masefield's sea ballads, making the teacher's failure to explore the seas more poignant; Robert Minhinnick's 'Yellow Palm', the only strongly-rhymed poem in his reading, uses the form's familiarity to temper the political anger that it contains. It is also a form that can survive the bending of its rules, as in the case of Causley's 'Miller's End' - this has tetrametric lines throughout, but retains the flavour, the forward motion of the form. However, Sebastian Barker's poem 'The Articles of Prayer', while it does use the ballad metre, is lacking a narrative and would therefore not normally be called a ballad.