opisthography

from The Century Dictionary.

• noun The practice of writing upon the back of anything; especially, writing on the back as well as the front of a roll of papyrus or parchment. See opisthograph.

from the GNU version of the Collaborative International Dictionary of English.

• noun rare A writing upon the back of anything, as upon the back of a leaf or sheet already written upon on one side.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A writing upon the back of anything, as upon the back of a sheet already written upon on one side.