One of the most confusing sets of regional terms we learn in the beginning of Anatomy and Physiology is "crural" versus "sural". Most medical dictionaries are pretty clear on "sural" - pertaining to the posterior lower limb. Some people call that the calf area of the leg. The sural nerve travels here.
What some textbooks don't seem to agree on is the use of the word "crural". Most definitions give "pertaining to the leg". However some of those same texts make the not-so-helpful clarification of the words "arm and "leg" into terms for the arm and forearm, and thigh and leg.So if "arm" really means the upper arm, then does "leg" really mean the upper leg?
Some textbooks would say yes, crural includes "pertaining to the leg or thigh" as a more complete definition. But then a figure in those same texts point to the front of the lower leg when using "crural".
Here is my take: If we use the arm analogy, then arm:forearm as crural:sural. In this case, crural refers to the upper leg and sural the lower, specifically the posterior lower area of the leg. You could get by with using "crural" to describe the entire leg, however, and use "sural" when specifically referring to the calf (posterior lower leg).
Does this all seem like semantics? Probably it does, but isn't all vocabulary semantics? We want to try to use correct terminology because that is the only way to communicate across distance - like in writing. When a nurse writes notes that a doctor later reads, everyone needs to be on the same page with what the words mean. If you see these particular terms, you might want to ask for clarification. Apparently different textbooks teach this term in different ways!