Okay, definitions...
From Urban Dictionary:
1. Movie, Book, or other type of publication with lurid subject matter, such as crime. Often shocking subjects portrayed as non-shocking.
2. A form of literature that originated in 1930's magazines. It features relatively simplistic and often lurid tales, with much action and little psychological thrills.
Other websites may define it differently, including bits about "larger than life characters".
I sum it up like this: Pulps were cheaply made, and churned out rapidly to fill consumer demand. The stories were simpler, with less convoluted plots, because the writers didn't have the time to be very literary.
What you end up with is something that is a quick read, with lots of action.
Men's Adventure books, particularly in the 1980s, were very similar, but they were slower paced in my opinion.
Thrillers and Mystery and suspense just don't capture that frenetic, reckless writing style the pulps had. Authors have more time to polish their prose.