SSD stands for Solid State Drive, a type of storage similar to traditional hard disk drives that uses flash memory to store data. SSD drives use memory similar to USB flash drives, in that they store data even when there is no power to the device, only at higher speeds.
Hybrid drives use both traditional hard disk and solid state storage, creating a drive that stores frequently used data in the faster solid state portion of the drive, leaving bulk storage to the hard disk. Some SSD units also use DRAM, a memory type similar to that used by computer programs, which allows for faster access to data. These types of drives often require constant power or have built in batteries to protect against any data loss, as the memory only stores data for as long as power is present.