SEO is the process of optimizing webpages to increase their ranking in search engine results. The Google Hummingbird algorithm aims to better understand user search queries by taking into account contextual elements like location and the intent behind questions. It uses Google's knowledge graph to provide more relevant responses to complex queries. PageRank is Google's method to determine a page's importance - important pages receive a higher PageRank and rank higher in search results. Factors like backlinks, relevant content, and keywords impact a page's PageRank. The document provides examples of how PageRank is calculated using a mathematical formula and transition matrix.