A poem of serious reflection on grief is an:

1. An elegy is a poem or song of serious reflection. 2. It expresses melancholy, grief or sorrow. 3. An ode praises, a ballad tells a story, and a sonnet has fourteen lines. **Why not the others:** An ode praises, a ballad narrates, and a sonnet is defined by its fourteen lines. _Source: Wikipedia, "Elegy", section "introduction" (revision 1376870908)_