According to their web site at http://www.spamcop.net, SpamCop is a "service for reporting spam".
They also maintain the "SpamCop Blocking List", aka SCBL. This blocking list (sometimes also called a blacklist) can be used by ISPs to refuse mail from servers which are on the SCBL.
Unfortunately ISPs who reject mail based on a SCBL listing will lose lots of legitimate mail. From the SpamCop web site:
So how does a server get listed on the SCBL? Unfortunately, as SpamCop says, it's easy. They honor "spam reports" from any of their customers. So anyone who receives mail and then reports it as spam can cause the sending server to wind up on the SCBL. Companies like DataBack who host discussions lists with thousands of subscribers see this problem frequently, when unsophisticated subscribers decide to report something they don't like as spam.
Fortunately a listing on the SCBL is short-lived. SpamCop keeps a particular server on the SCBL for only 24 hours unless there are continuing reports.
Unfortunately if your ISP is one which discards mail based on an SCBL listing, then you will lose legitimate mail. See http://www.spamcop.net/bl.shtml?126.96.36.199 for a description of the many reasons SpamCop might block legitimate mail.
A more technical description of the SCBL can be found at http://www.spamcop.net/fom-serve/cache/297.html