Pulp fiction / magazines (often referred to as "the pulps") are inexpensive fiction magazines published from 1896 through the 1950s.
The typical pulp magazine was 7 inches (18 cm) wide by 10 inches (25 cm) high, 0.5 inches (1.3 cm) thick, and 128 pages long.
Pulps were printed on cheap paper with ragged, untrimmed edges.
The term pulp derives from the cheap wood pulp paper on which the magazines were printed.
Although many respected writers wrote for pulps, the magazines are best remembered for their lurid and exploitative stories and sensational cover art.
Modern superhero comic books are sometimes considered descendants of "hero pulps"; pulp magazines often featured illustrated novel-length stories of heroic characters, such as The Shadow, Doc Savage and The Phantom Detective.
See more at http://en.wikipedia.org/wiki/Pulp_magazine