non-orientable
/ˌnɒnɔːrɪˈɛntəbl/ /ˌnɒnɒrɪˈɛntəbl/Mathematics
adjective
Of a manifold: not having a well-defined global coordinate system; not orientable; specifically (of a surface) such that a figure in the surface can be continuously transformed into its mirror image by taking it round a closed path in the surface.
Origin
1920s; earliest use found in Transactions of the American Mathematical Society. From non- + orientable.