Solid State Disk (aka Solid State Drive or SSD) is a data storage device that uses NAND Flash to store persistent data. Mainly it is made to replace the conventional HDD.
Unlike conventional Hard Disk Drive (HDD), which uses spinning platter and mechanical magnetic head, SSD is based on NAND Flash. Without moving parts, SSD can eliminate seek time, latency and other electro-mechanical delays caused in HDD.