Final answer:
The term 'serial killer' was first coined around the turn of the twentieth century but did not become conventional until the 1970s.
Step-by-step explanation:
The term 'serial killer' was first coined around the turn of the twentieth century. It was used in reference to three pandemics in a book by Simpson in 1905. However, it did not become conventional until the 1970s. The term "serial killer" was first coined in the latter part of the 20th century. It emerged to describe a certain type of murderer who commits a series of homicides over a period of time. Although the concept of a person committing multiple murders is not new, the specific term to describe this type of crime was not popularized until much later. The exact timing of the term's coinage is not pinpointed in the provided references, but its use was certainly established by the late 20th century.