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.
This composition is in fugue form. It has a principal theme called 'subject' which recurs in multiple voices. It is composed according to the element of counterpoint.
theme
Fuge ((fug)itive). As in refuge (Re(fuge))
The main idea of a poem is called its theme. This theme often represents the central message or insight that the poet is trying to convey through the poem.
This is called the theme.
Sen to Chihiro
Theme
the Ballad of the Goddess
"Start Line" by COACH☆
The main tune is called the "head." It establishes the chord structure and overall theme.
It's officially called "Star Wars Main Title."
It's just called the main theme, or title theme. There's no specific fancy name. If you need to look it up to listen to ever just search "Skyrim Main Theme"