Read custom search plugin for WordPress for more information.
Did you know that the default WordPress search engine isn’t really that efficient (and awesome) as the rest of WordPress?
Although the search is available as a function in WordPress, it does not search custom post types and taxonomies.
This means that if you have a custom post type as “Book” for a book review website, then the default search isn’t going to look there.
Thankfully there are a host of awesome plugins that help you implement a powerful search solution in your WordPress site, with varying degrees of specificity.