The rank or ranking of a web page in a search engine index is a number indicating where that page is displayed in the organic results section on a search results page.
For example, on Google, the first search results page generally shows ten URLs, starting with the #1 ranking page at the top, and the #10 ranking page at the bottom. In this example, if you ranked #11 for a specific search phrase, you would appear at the top of the second page of results.
Rankings are often used as a metric to measure the success of SEO efforts; ideally search optimization for specific phrases will result in the increased rank of a website or page for that term.
In the SEO industry, a 'redirect' is a reference to a search engine friendly redirection from one web page or website to another web page or website.
If the address for a particular page or resource changes, it is always advisable to redirect search engines and visitors to the new address using a redirect. If the address for a resource changes and a redirect is not implemented, the user or search robot will encounter an error page, and not reach their desired destination.
Search engine friendly redirects are implemented by using a server status code. The status code for a search engine friendly redirect is '301,' so a redirect may also be called a 301 redirect, or a 301 search engine friendly redirect.
Also known as a spider or web crawler - a computer program or script that automatically navigates the web, viewing pages, archiving them, and referencing them for use in search engines and other projects.