One of the short lines used on maps to shade or to indicate slopes and their degree and direction. 

In a sentence: 
When John was driving in the mountains, he kept looking for the physical presence of hachures, and eventually crashed.

In a different sentence:
Looking at the map, Sandra was constantly distracted by the hachures, which she thought were both “cool” and “like, totally confusing…” at the same time.

A sad poem about a teenage outcast: 
Always paranoid, never sure,
Noticeably shy, somewhat demure,
Tina was as invisible as a hachure…

Fact:
In 1799, topographer Johann G. Lehmann is thought to have been the first to design a hachure map.