Pulps were periodicals printed on uncoated pulp wood paper. It was a medium that thrived between 1895 and 1950. Pulps specialized in popular fiction, and selling at a price of 25 cents, were more affordable than hard cover books ($3.00 to $6.00). The introduction of comic books and mass market paperbacks in the USA in the mid-to-late 1930s started a competition with pulps, which contributed to their decline.
True Detective, Stag, Saga, and many more men's adventure titles from the 1950s onward are magazines, not pulps. However, the writing style in many stories in those magazines can be called "pulp fiction."
Weird Tales, Black Mask, The Shadow, Doc Savage, The All-Story, Astonishing Stories, Adventure, are prime examples of pulps.