A curvature such as Gaussian curvature which is detectable to the "inhabitants" of a surface and not just outside observers. An extrinsic curvature, on the other hand, is not detectable to someone who can't study the three-dimensional space surrounding the surface on which he resides.
Intrinsic Curvature
See also
Curvature, Extrinsic Curvature, Gaussian CurvatureExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Intrinsic Curvature." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/IntrinsicCurvature.html