Crawl budget refers to the number of pages a site is allowed to request that Google crawls on a daily basis. It is important because exceeding the crawl budget can lead to pages not being indexed. The document provides tips on how to identify a site's current crawl rate, issues impacting crawl budget like errors and duplicate content, and strategies for optimizing demand and capacity such as improving site speed and creating fresh content regularly. The goal is identifying any crawl issues and optimizing the crawl budget to have the most important pages indexed.