Pulps can be generally considered to be of three types. The best known is the traditional pulp magazine, like The Shadow. These often have covers slightly bigger than the actual magazine pages, causing the edges of the covers to easily tear and fray. (The sizes of these can vary, of course.)
The second kind of is the pulp magazine. These were sometimes of normal magazine size, although size could vary from small to large. They were printed on cheap paper, though.
The third kind is the pulp paperback, again since it was printed on poor-quality paper.
Sometimes I think the term pulp is not just a description of the paper but some kind of judging of the types of articles and stories that were contained, sort of a form of classicism, with the pulps considered by some to be appealing to the lower classes, although some of the greatest authors, particularly in crime and science-fiction pulps, wrote for them.
Anyhow, I've gotten very interested in them. Sometimes the stories are good, sometimes they are pretty darn bad. A lot of the ones I have gotten have ads relating to World War II, and many of the romance pulps have stories related to the war. It's also interesting to look at the old ads (Charles Atlas, false teeth for women, train in radio, electronics, etc.) It was a much more innocent time, then.