VelociRaptor is a mechanical hard drive, just a really fast one. SSD stands for "solid state drive" and as the name implies, there's no moving parts (and no RPM to compare to hard drives) - the technology used is similar to that used in USB thumb drives, only just better (faster and more reliable). Since there's no moving parts and latencies involved with physically moving things to access data, SSDs are generally a lot faster (beware of the cheap ones, though).
Also, SATA is simply the type of connection the drives use. SSDs use SATA as well.