The baseline is a term used in European and West Asian typography meaning an imaginary line upon which the characters of a font rest.
The descenders of characters like g and p extend below this line. Glyphs with rounded lower and upper extents like C or 3 slightly extend below it.
East Asian scripts have no baseline. Their glyphs are placed in a square box without ascenders or descenders.
- Baseline on Wikipedia
- CSS Box Alignment on MDN