Printing on one side of paper that can be seen on the other side.
The generally undesirable property of a substrate that permits underlying markings to be seen
See opacity. When a printed impression on one side of a sheet is visible through the other side of the paper. 
The degree to which printing is visible through paper due to the low opacity of the paper.
The generally undesirable property of a substrate that permits underlying markings to be seen and may adversely affect read rate.
A problem that occurs when the printing on one side of a sheet is seen from the other side.