the semantics are a bit hard - it's the average mean curvature over the parcellation unit On Tue, 27 Jan 2009, Allison Stevens wrote:
The mean curvature for that particular parcellation.
There is a slide demonstrating curvature here: https://surfer.nmr.mgh.harvard.edu/fswiki/ArticlesSlidesAndPosters
Under the Slides section, the one called "Anatomical Analysis with FreeSurfer". It's slide #14.