The symphonic poem was the invention of Franz Liszt and was sometimes called a Tone Poem, especially when it was based on a poetic idea. The form comprises one continuous movement and is usually based on the principle of variations on a theme, or contrasting themes, that are inspired by a program or a literary idea. It is a transformation of themes in which they retain their identity through various stages and forms.
(See the article: The Symphonic Poem)