What is an SIC type rating?
It's an ICAO requirement, basically it's just official documentation showing that you've been trained and are  competent to act as SIC in a given airplane.

ICAO is an organization that standardizes regulations and procedures among the participating countries (close to 200 if I recall).  If you fly as SIC internationally you'll probably need an SIC type rating.

The rating is almost the same as a PIC type rating, except the rejected takeoff and taxi requirements (and maybe some others) don't have to be met.  It's basically a formality for any airline first officer as they will have met all the requirements just by going through the airline's training.