SSD = Solid State Drive
SSHD = Solid State Hybrid Drive
HDD= Hard Disk Drive
A HDD is a traditional spinning hard disk. Cheap to buy, but effective.
A SSHD is a HDD with a small amount of SDD in it. The drive itself desides when/how to use to SSD.
A SSD does not have any moving part and is has MUCH faster read/write speeds.
If you are using any databases, SSD can make a big difference.