Answer:
These two paragraphs placed on an A4 or Letter-sized sheet of paper make up 5% coverage:
"For the purpose of cartridge yield measure, almost all printer manufacturers base their black ink/toner cartridge yields on 5% coverage. This means only 5% of the whole page is covered with ink or toner. 5% coverage implies basic type with no bold characters, no graphics and no pictures.
CMYK toners for color laser printers and copiers base their cartridges yields on 20% to 35% coverage (5% to 7% per color). In reality, if a document had a 100% fill, there would be 400% coverage. Tri-color inkjet/toner cartridges base their page yield on 15% coverage (5% per color)."
(Taken from http://blog.tonercartridgedepot.com/2008/01/17/what-5-percent-coverage-page-looks-like/)
This shows several thumbnails including one with a 5% example: http://blog.hbsx.com/what-is-print-coverage-why-you-should-care