What is an SSD?

SSD - a storage device containing nonvolatile flash memory, used in place of a hard disk because of its much greater speed.
"a decent SSD offers arguably the biggest jump in performance for your general PC experience"

A solid-state drive (SSD, also known as a solid-state disk) is a solid-state storage device that uses RAM to store data. SSDs have no moving mechanical components. This distinguishes them from traditional hard disk drives (HDDs), which contain spinning disks and movable heads. Compared with hard disks, SSDs are typically more resistant to physical shock, run silently, and have lower access time and lower latency. Fewer moving parts also typically result in lower power consumption and therefore better overall battery life in consumer laptops/netbooks.