What is a key difference between serif and sans-serif fonts?

The key distinction between serif and sans-serif fonts lies in the presence of "serifs," which are small decorative lines or extensions at the ends of a letter's strokes. In serif fonts, these embellishments are present, lending a traditional and formal appearance to the text. This characteristic can enhance readability in printed materials, as the serifs guide the flow of reading. Sans-serif fonts, on the other hand, do not feature these lines; thus, they tend to have a cleaner and more modern look. This simplicity is often chosen for digital displays and user interfaces, where readability at various screen sizes is crucial.

The other options mention attributes like size, weight, and decoration without addressing the fundamental design feature that distinguishes these two font families. Hence, the emphasis on the presence or absence of serifs directly captures the essence of what differentiates serif from sans-serif fonts.