Original: A symphonic poem or tone poem is a piece of orchestral music in a single continuous section (a movement) in which the content of a poem, a story or novel, a painting, a landscape or another (non-musical) source is illustrated or evoked.
Simplified: A symphonic poem or tone poem is a piece of orchestral music which has a story attached to it or describes something such as poem or a painting or any idea which is not music.