Usually called a "theme".
The Doctrine of the Affections is the Baroque idea that only one specific feeling should be communicated throughout a piece of music.
A motif is a small musical idea. It's generally repeated throughout a piece of music and can be sequenced (moved up and down in pitch).
A Baroque idea that only one feeling should be communicated in a piece of musicAPEX ^^
emotion, feeling
Wagner's idea that an Opera that has continuous music throughout with a primary goal of symbolizing the drama was called music drama. He also broke the record for opera length with his piece Der Ring des Nibelungen -- it took four nights to perform, with a total of about 15 hours,
The "A" melody
This is as theory in musical aesthetics widely accepted by the Baroque composers in the Baroque era. The "Doctrine of the Affections" was first promulgated at the end of the Renaissance. It is the result of many minds at work so it couldn't be attributed to a sigle writer.
Symphonic poem
Theme Apex
Excerpt: "a short extract from a film, broadcast, or piece of music or writing." So the idea conveyed in the definition of "excerpt" is the idea that an excerpt is a small piece of information which can be useful to convey opinions, facts and ideas. Your use of the word "the" conveys to me that you were being specific but at the same time your was question vague.
The main theme of a fugue is called the "subject." It is the main melodic idea that is introduced at the beginning of the piece and is then developed and imitated throughout the composition.
Rhyme means something that sounds the same as another another word or has a similar ending you normally find a rhyme in poems. Theme means the subject or idea of the piece that runs throughout the piece.