Mirror domains or mirror sites

Multiple copies of web sites, often on different servers, with the exact same, or similar, content. Used to artificially boost link popularity and search engine visibility are considered search engine spamming.

Mirror pages

Multiple copies of web pages, often on different servers, with the exact same, or similar, content to boost link popularity and Search Engine Visibility should not be incorporated when optimizing your website.

Since search engine spiders have no way of determining a person's intent, one way they eliminate spam is by using duplicate, or "dupe", filters to eliminate redundant content. In an ideal situation, a search engine spider might detect duplicate content and eliminate one of the domain names from the index. Most likely, the domain that is eliminated is the domain that has the most Link Popularity and Search Engine Visibility. In other words, the domain that has the most link popularity and search engine visibility, will be the one that usually gets banned and no longer is featured in the search engine results pages (SERPs).