FCL means "Full Container Load" referring to one full shipping container box which are on average 20" (20 feet). So this is referring to shipping cost where you are shipping enough to use one full container, rather than shipping an amount smaller than this.

I have no idea what FCL means. Haha! I do know a "carton" is usually a container for liquids like milk. It's usually made of cardboard or coated paper.

When you ask a question, particularly one with acronyms, it really helps to give the context of your question.