This document defines e-commerce and discusses its types. It describes e-commerce as business transactions conducted over the Internet and identifies the main types as B2B (business to business), B2C (business to consumer), C2C (consumer to consumer), C2B (consumer to business), and m-commerce (mobile commerce). The document also outlines some key aspects of each type and discusses the importance of e-commerce, supply chains, direct sales over the web, and e-commerce payment systems.