What literary term refers to a poem or song expressing lamentation?

The term that accurately describes a poem or song expressing lamentation is "elegy." An elegy traditionally reflects sorrow or mourning, often centered on the loss of someone or something significant. It embodies deep reflections on grief and the process of coming to terms with loss, making it distinct in its focus on themes of mortality and remembrance.

In contrast, a ballad typically tells a story and is often narrative in nature, commonly incorporating elements of folklore. Although ballads can contain themes of longing or tragedy, they do not specifically serve the function of lamentation like elegies do.

A sonnet, which is characterized by its specific rhyme schemes and a focus on themes such as love or beauty, does not inherently reflect lamentation or mourning. Lastly, an ode is a lyrical poem that expresses praise, admiration, or deep feeling about a subject; while odes can convey emotional depth, they do not necessarily center on lamentation.

Thus, the correct answer is rooted in the specific focus of elegies on mourning and loss, distinguishing them from the other forms of poetry listed.