This document discusses the different types of e-commerce systems, including B2B, B2C, C2B, and C2C. B2B refers to business-to-business e-commerce, which makes up about 80% of e-commerce transactions. B2C involves businesses selling directly to consumers online. C2B allows consumers to post projects and solicit bids from companies. C2C enables individuals to buy and sell from each other using online payment systems. The document also briefly mentions several other types like m-commerce, government-to-government, and government-to-citizen e-commerce.