What does is the a and b section called in musical form?

In musical form, the "A" section is typically referred to as the "theme" or "statement," while the "B" section is often called the "contrast" or "episode." Together, these sections can form various structures, such as AABA or ABAB, where the A section presents a main idea and the B section provides contrast or development. This structure is commonly found in genres like Classical Music and popular song forms.