What does the term 'stem' refer to in the context of aleter?

In the context of calligraphy, particularly when discussing letterforms, the term 'stem' specifically refers to the main vertical or diagonal stroke of a letter that contributes to its overall structure. This element is crucial because it provides the letter with its foundational stability and is often one of the most prominent features seen in various typefaces.

For instance, in letters like 'b', 'd', 'h', and 'k', the stem is what makes up the primary body of each character, extending upwards and helping to define its shape. Understanding this aspect is essential for calligraphers, as focusing on the correct formation of the stem enhances the readability and aesthetic appeal of the letters they create.

The other options, while related to aspects of letters and calligraphy, do not accurately capture the essence of what a 'stem' is. The base of a letter pertains to its bottom part, the upward stroke can refer to different elements in various letterforms but does not encapsulate the full meaning of 'stem', and the flourish is an ornamental touch that may appear in calligraphy but is distinct from foundational structures like the stem.