Here is a great article on slab serifs.
In typography, a slab serif (also called mechanistic, square serif or Egyptian) typeface is a type of serif typeface characterized by thick, block-like serifs. Serif terminals may be either blunt and angular (Rockwell), or rounded (Courier). Slab serif typefaces generally have no bracket (feature connecting the strokes to the serifs). Some consider slab serifs to be a subset of modern serif typefaces.
Because of their bold appearance, they are most commonly used in large headlines and advertisements but are seldom used in body text. One recent exception to the general lack of the use of Slab Serif in body text is Egyptienne, a font designed for the The Guardian newspaper in the UK, which is used throughout the paper and within its body. Another common exception to this rule is in the use of monospaced text, many fonts for which are modeled on the typefaces used by typewriters. Though widely utilized in the field of computer science due to their fixed-width nature, the everyday use of typewriter-like fonts is declining in the wake of electronic publishing and the spread of electronic reading devices.
As printed material began to branch out from the familiar realm of books, new typefaces were needed for use in advertising, posters, and flyers. Slab serif printing type was first commercially introduced by Vincent Figgins under the name Antique, with copies of specimen dated 1815 and 1817.
Following Napoleon’s Egyptian campaign and dissemination of images and descriptions via publications like Description de l’Égypte (1809) an intense cultural fascination with all things Egyptian followed. Suites of contemporary parlor furniture were produced resembling furniture found in tombs. Multicolored woodblock printed wallpaper could make a dining room in Edinburgh or Chicago feel like Luxor. While there was no relationship between Egyptian writing systems and slab serif types, either shrewd marketing or honest confusion led to slab serifs often being called Egyptians, and many early ones are named for the subject: Cairo, Karnak, and Memphis. The common metonym “Egyptian” is derived from a craze for Egyptian artifacts in Europe and North America in the early nineteenth century, which led typefounders producing Slab Serifs after Figgins’ work to call their designs Egyptian. However, the term Egyptian had previously been used to describe sans-serif types in England, so the term ‘Antique’ was used by British and American typefounders. The term Egyptian was adopted by French and German foundries, where it became Egyptienne.