Have you ever searched for something and found a link that wasn't quite what you were looking for but was reasonably close? If you were using an Internet search engine such as Google, then you may have tried the "more like this…" link next to a search result. Some sites use other language like "find similar..." or "related documents…" As these links suggest, they show you pages similar to another page. Solr supports more-like-this (MLT) too.
The MLT capability in Solr can be used in the following three ways: