What Is Font Weight?
Font weight is the thickness of a typeface's strokes, from thin and light through regular and bold to black. Heavier weights draw attention and create hierarchy; lighter weights feel airy and refined. Weights are often numbered 100–900 in CSS, where 400 is regular and 700 is bold.
A family with many weights gives designers fine control over emphasis and hierarchy without changing typeface, keeping a layout unified.
Avoid "faux bold," where software algorithmically thickens a regular weight — it distorts the letterforms. Use a real bold cut, or a variable font's weight axis, instead.