What part of a lowercase letter refers to its main structure?

The part of a lowercase letter that refers to its main structure is identified as the body. In calligraphy and typography, the body encompasses the bulk of the character's form, excluding any additional elements such as serifs or decorative features. It represents the primary visual area that contributes to the overall shape and readability of the letter.

Understanding the concept of the body is important because it lays the foundation for how letters are perceived as cohesive units of text. While other terms like the stem (which is a specific vertical line that forms part of many letters), counter (the enclosed space within certain characters), and branching line (which may refer to lines that extend from a letter's body) are relevant in discussing various aspects of letterforms, they do not encompass the entire main structure in the same way that the body does. Hence, recognizing the body as the core structural component allows for a better grasp of letter design and its significance in calligraphy.