SSD stands for Solid State drive. It is latest type of storage device used by most of the technical upgraded hosting service providers.
The traditional hosting uses the Disk type storage devise in which s disk moves and data is stored or retrieved by a device "Disk read write head" . It is more like a mechanical device.
In SSD there is no such moving device. The read & write activities are electronically managed.
SSD is far superior in today's trend and your must look for a SSD web hosting if you are currently planing to buy a new web hosting.