These have been named after old monks’ sandals.
A monkstrap or monk shoe is a style of shoe with no lacing and easily closed by buckles and straps. It often has an extra decorative toecap, broguing, and it can be made of suede or vegetal-tanned calfskin.
It is a moderately formal shoe, so it is less formal than a full Oxford but more than an open Derby, so it is appropriate for business meetings and more informal occasions as well. We can state that this is one of the main categories of men's shoes.