SSDs are very fast, and until recently, their storage capacity was limited relative to old-fashioned mechanical spinning HDDs. They were also rather pricey.
You probably haven’t heard quite as much about SSHDs: hybrid mechanical hard drives with a small amount of SSD-type storage built-in. The idea here is that the SSD part of the drive can be accessed very quickly, so it acts as a very fast buffer between your puter and the slower mechanical part of the drive.
The result? SSHDs are faster than a mechanical HDD, not as fast as an SSD, but still offer 2TB, 4TB, or even more storage space – all at an affordable price.