Typographically, the vertical line or stem defines each letter form.
Stem is found in the uppercase and lowercase letters like A, B, H, k, l, m, and n, which constitute the spine of each letter, and also the vertical stroke that distinguishes one letter from the others. In terms of design style or aesthetics of typeface, length, width, and thickness may differ.
The stems of lowercase letters such as p and q extend above and below the median line (descenders and ascenders, respectively). These help keep balance and equal spacing and avoid unbalanced or awkward spacing.
When creating typefaces, designers ensure that letterforms have visual harmony as it is paid particular attention to. They try to balance the stem weight and other factors such as terminals, serifs, and crossbars of letters.
Therefore, stems create proportions upon which measures such as x-height (the measure of lowercase letters) and cap height, which defines the uppercase letter heights, are based, ensuring a readable text within a typographic composition.
Stems are, in fact, an integral part of typography, which creates the form of the typeface, allows its proper functioning, and gives it aestheticism.