What do we call the strokes that extend up and down in letters?

The term used for the strokes that extend up and down in letters is "stem." In typography and calligraphy, the stem refers specifically to the main vertical and sometimes horizontal strokes that form the structure of a letter. For example, in the letter "b," the long vertical line that creates the main outline of the letter is its stem. This component is essential in defining the character and overall shape of a letterform.

Understanding the role of the stem is crucial for effective calligraphy, as it contributes to the balance and proportion of the letter. While other options may refer to different parts of a letter, such as the "body," which often describes the overall shape, or "counter," which indicates the enclosed space within certain letters, they do not specifically denote the primary vertical or horizontal strokes. Therefore, recognizing the stem is fundamental to grasping the anatomy of letterforms in both calligraphy and typography.