SSD or a Solid State Drive is a storage device that is normally located inside the body of a Laptop PC or a Desktop PC. Enterprise Solid State Drives can be found in the servers and workstation computers. In terms of functionality, SSD plays the same role as the classic hard drive (HDD). They both are used to store data for long term retrieval. SSDs are fast because of flash memory technology that is used in them. SSDs are different from HDDs in that they don't have the spinning discs that spins and have no movable part that need to move so the read-write process can occur. It's simply a solid part with nothing moving (no spinning discs, or moving heads) when you will look at it from outside. Solid State Drives come in various forms. We will discuss about them shortly.
There are various types of SSDs available like SATA 2.5" SSD, M.2 2280 (or 2230 and 2242) PCIe NVMe SSD, M.2 2280 SATA SSD, and mSATA SSD. If you are looking to upgrade SSD on your laptop or desktop, refer to the manufacturer product manuel to find out which type of SSD does your laptop or desktop. Normally, manuel contains detailed information about the compatibility of SSD as well as what's the max SSD capacity which your laptop supports.