(describes something curved with many twists and turns)
The word tortuosity (adjective: tortuous) indicates the quality of
a curving object of having many curves and/or twists. It can be
used to describe the path of a river, and is sometimes used to
describe the channels through a porous material.
Some measures have been devised to quantify it,
necessarily adopting a more specific definition,
probably adapted to a specific type of issue.
One (simple) measure:
τ = L/C
τ - tortuosity (in this case, arc-chord ratio).
L - length of the curve (i.e., arc length).
C - straight-line distance between the ends of the curve.