This document discusses various aspects of digital marketing and online advertising. It defines digital marketing as promoting brands using online channels like websites, apps, social media, and other forms of digital media. Viral marketing is described as using social networks to increase brand awareness through shared content. The AIDA model of marketing is explained as the stages of awareness, interest, desire, and action. Metrics on the growth of the digital marketing industry are provided, and the advantages and challenges of digital versus traditional marketing are compared.