What is the term for a sad or mournful poem?

The term for a sad or mournful poem is "elegy." This type of poem is specifically written to lament the loss of someone or something, expressing deep sorrow and reflection on the themes of death and mourning. Elegies often pay tribute to the deceased and explore feelings of grief, making them distinct from other poetic forms.

Odes, while also a type of lyrical poetry, typically celebrate or praise an event, person, or thing and do not focus on sorrow. Sonnets are structured poems that often explore themes of love, nature, or time but do not inherently convey a mournful tone. Ballads, on the other hand, are narrative poems that tell a story, which may include themes of tragedy but are not exclusively sad or mournful in nature. Therefore, elegy is the correct term for a poem that specifically expresses sorrow.