Mikiko Lockwood in an article on The Hosta Library titled,
A Little About Japanese Hosta Terms defines the term urajiro
as white-backed or white underside and the term oba or ooba as large leaf or 'Oba Gibōshi' which is the Japanese name for the species H. montana.
Many hostas in Japan have been given the
simple name 'Urajiro' which would indicate that
the plant has a whitish color on the bottom
foliage. There are at least 5 such plants
with that name, all from different species