What are the most common facets of a search engine and how does it affect SEO?
To better optimize your site, you need to understand the basic facets of a search engine and how each one interacts with your site.
For instance, there are spiders and crawlers and both do different jobs.
The spider downloads your site, while the crawler follows all links. The concept of Indexer is an algorithm that looks at your web data which was collected previously and makes a determination of it's worth.