According to Arizona State University, Robert Hooke used the term "cells" in reference to small biological organisms because their structure reminded him of monks' rooms or "cells." The term stuck, and these organisms are still referred to as cells today.
In 1665, Hooke, an English natural philosopher, published "Micrographia," the first book to contain illustrations of the microscopic world. In the book, Hooke used the term "cell" to describe the microscopic structure of a thinly sliced piece of cork. As cameras had not yet been invented, Hooke hand drew all the illustrations in the book in amazing detail and included instructions on how to build a microscope like the one he used when he wrote and illustrated the book.