The pulps were magazines printed on cheap wood-pulp paper. Such prozines dominated SF publishing from its beginnings through the 1940s, largely dying out over the ’50s. The format was characterized by unsophisticated and usually formulaic adventure stories. Nonetheless, modern SF grew from those pulp beginnings.
Inexpensive fiction magazines published from 1896 through the 1950s, the typical pulp magazine was seven inches wide by ten inches high, half an inch thick, and 128 pages long. Pulps were printed on cheap paper with ragged, untrimmed edges.