Source: A 1931 dictionary
Khol (खोल्) is the Nepali word for the grooves running the base of a khukurī blade. They are present on the vast majority of antique khukurī.
Alternatively, it can mean scabbard, sheath; any covering.
Well, not any. The khukurī scabbard specifically is called dāp (दाप्). 1
A mid 19th century khukurī with khol.
The are the two narrow grooves running along the back of the first portion of the blade.
For a complete overview of khukurī terminology, see my article: A Nepalese khukurī glossary.
1. Sir Ralph Lilley Turner; A comparative and etymological dictionary of the Nepali language. London: K. Paul, Trench, Trubner, 1931.