Dr. Bill's definition is from something called the Brainy Dictionary.

http://www.brainydictionary.com/words/co/cop148049.html

also

"Cop- the conical ball of cotton or any yarn wound on the spinning frame."

http://www.cottontown.org/page.cfm?pageid=328

also

"A Form Of Yarn Package Spun On A Mule Spindle. The Term Can Also Be Used To Describe A Ring Tube."

http://www.fibre2fashion.com/glossary/glossary3.htm

also

"A form of yarn package such as is spun on a mule spindle, that is essentially self-supporting. A weft-cop, as used at Holdsworths on face-to-face looms until 1980, was a cop of tightly wound yarn of such a size that it could be used directly in the loom shuttle. These cops were very difficult to handle without damage, and caused a great deal of problems in terms of wasted material and the maintenance cost of the cop-winders. The whole process was made obsolete with the replacement of machinery with shuttle-less looms from Güsken in the early 1980s."

http://www.holdsworth.co.uk/history/Cyclopaedia/c.html