What is a serif in typography?

In typography, a serif refers to the decorative stroke that extends from the ends of the strokes of a letterform. This embellishment is commonly found in certain font styles, such as Times New Roman or Garamond. The presence of serifs can enhance the readability of text, especially in printed materials, by guiding the reader's eye along lines of text. Serif fonts are often perceived as more traditional and formal, making them a popular choice for printed publications, books, and formal documents.

The other options describe different elements related to typography but do not convey the correct definition of a serif. A straight line is not specific to serifs, a type of paper pertains to the medium rather than the lettering style, and spacing letters is a typographic technique unrelated to the decorative strokes on letters themselves. Understanding the definition of a serif helps in recognizing the characteristics and applications of various font styles in design and typography.