Questions about the small lines attached to the end of a stroke in a letter or symbol, such as when writing is separated into distinct glyphs for a typewriter or typesetter. A typeface with serifs is called a serif typeface (or serifed typeface).
Serifs are stylistic embellishments, comprised of small lines appended to the end of a stroke in a letter/symbol. These embellishments are utilized by the font, typically for distinction. Serif fonts, aka Serif typefaces, are thus fonts that have stylistic small-lines following strokes in the typeface.
Serif literally means "with feet" in Latin, so when applied to typography, the small-lines appended after strokes are "little feet".
Sans-Serif fonts, the arch-nemesis of Serif fonts, literally means "without feet" in Latin.
See also sans-serif