SSD stands for solid state drive (some people say solid state disk). It is the part of a computer or phone that stores your files and programs — the things that stay there after you switch the power off. What makes it different from the older hard disk drive (HDD) is that nothing inside it moves: an HDD has a spinning metal plate and an arm that swings across it, while an SSD stores everything in memory chips. "Solid state" is just the engineer's way of saying "no moving parts." That is why SSDs are much faster to open files, silent, lighter, and harder to break if you drop the machine — and also why they cost more per amount of storage. Almost every laptop and phone sold now uses one. In everyday speech people just say "my SSD" or even "my drive." It is written in capitals and said letter by letter, ess-ess-dee.