My understanding is that, in a British newspaper, the copytaster, or copy-taster, would be a senior journalist who would look at the material coming in on the wire services (AP, UPI, Reuter, etc) plus stuff produced in-house and decide what should, and what shouldn't, go in the next edition of the paper.
My impression is that it's not an expression used in American journalism. (Few Google hits, not in Webster online (1).)
Is there a word in AmE that covers the same function? Or are US newsrooms organised in a way that the job simply doesn't exist?
(1)
http://m-w.com/