An HDD hard disk (Hard Disk Drive) is built with a magnetic coating (metal plate) where all data is stored. This data is written by a small needle that, like an old LP record, writes by physical contact. The big disadvantage of an HDD hard disk is that it is easily susceptible to shocks and impacts.
An SSD hard disk (Solid State Drive) is a newer type of hard disk. It stores data on a series of flash memory cards that work together and, unlike an HDD hard disk, are not built with moving parts. By choosing an SSD, you get a faster startup and a better experience. It can also withstand shocks and impacts better than HDD technology.
A Refurb® PC will typically be equipped with an SSD.