dedicated WordPress web hosting
WordPress is quite slow out of the box due to its flexibility and ability to connect with other applications. This problem gets worse if you overload the site with poorly coded themes and plugins.
But WordPress can be optimized to significantly improve site performance thus provide a better user experience and conversions.
Dedicated WordPress hosting companies are able to fine tune the server configuration to get as much performance out of WordPress as possible. This is something generic hosts aren't able to provide.