The baseline is the fixed invisible line that serves as the base for letters. The baseline is used as a measurement for line height and x-height.
Descendent characters such as lowercase g and p extend below the baseline, while rounded characters such as C and 0 extend slightly below it. In typography, the baseline exists in relation to other principal line terms, including:
The median (mean line) where letters like lowercase e and c end
Cap height, where capital letters exceed the baseline
Ascender height (ascent), to where the stem of b and h extends
Descender height (descent), to where lowercase g and p extend
The baseline grid is the vertical space between baselines in a text block, the size of which depends on the number of vertical pixels in the text box. Most typefaces adhere to a baseline. However, East Asian scripts don’t have a baseline since each glyph sits in a square box.
