A very common question. A lively discussion on this topic just 2 weeks ago:
http://ficoforums.myfico.com/fico/board/message?board.id=creditcard&message.id=44423&query.id=126972#M44423
It's really in the eyes of the beholder.
If you type in "sub-prime" in the search box, you'll get an idea of people's opinions of them.
Many ccc's offer both prime and sub-prime cards. Sub-primes are generally accepted as those cards with: low cr's; AF; monthly fee, high interest rates; short or no grace period.
Hope that helps
