What are compound light microscopes?
"Compound" is meant as "not simple".
A simple microscope consists of just one lens, possibly made up of different kinds of glass. The magnification is limited, although Anthony van Leeuwenhoek made some quite impressive discoveries with them. (https://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek).
A compound microscope makes a real, inverted, enlarged image of the object with one lens-set (called the objective). This image is then further enlarged by another lens-set, the ocular.
Compound microscopes are the norm today, while simple microscopes are usually called loupes (or thread counters).