What can be either 'serif' or 'sans serif'?

In typography, a serif is a small line attached to the end of a stroke in a letter or symbol. A typeface with serifs is called a serif typeface (or serifed typeface). A typeface without serifs is called sans-serif or sans serif, from the French sans, meaning "without". Some typography sources refer to sans-serif typefaces as "Grotesque" (in German "grotesk") or "Gothic", and serif typefaces as "Roman".

Serifs originated in the Latin alphabet with inscriptional lettering (words carved into stone in Roman antiquity). The explanation proposed by Father Edward Catich in his 1968 book 'The Origin of the Serif' is now broadly but not universally accepted: the Roman letter outlines were first painted onto stone, and the stone carvers followed the brush marks, which flared at stroke ends and corners, creating serifs. Another theory is that serifs were devised to neaten the ends of lines as they were chiseled into stone.