I’m trying to find out the correct term for this form of art:
It’s a type of halftone.
A halftone is where you take a continuos-tone image (like a photograph) and turn it into a one-color representation to enable printing. The most common type of halftone is made up of a grid of various sized dots (usually most noticeable in newspapers–where the dots have to be pretty big due to the poor quality of the paper). The size of the dots varies which makes it appear to be continuous tone from a distance. But there’s no reason you have to use dots. You can use any shape at all and a common one is variable width lines like this one. It was a really common design element in late 70s/early 80s logos as well. Perhaps one of the most memorable ones being Saul Bass’s death star logo for AT&T:
The easiest way to make this type of illustration is to use Photoshop’s halftone filter, which lets you choose ‘line’ as one of the shape options.