Very roughly a surface is orientable if it has two sides so that, for example, is
it possible to paint it with two different colours. A sheet of paper or the
surface of a sphere are examples of orientable surfaces. A Mobius strip is a
non-orientable surface: you can build one with a strip of paper (twist the strip
and glue end together to form a ring) and verify that it has only one side: it is
not possible to paint it with two colours.

'I believe there is no philosophical high-road in science, with epistemological signposts. No, we are in a jungle and find our way by trial and error, building our road behind us as we proceed.'
Max Born
(1882-1970)