A standard for RAM chips designed specifically for mobile (battery-powered) devices like phones and laptops. It uses less power than RAM used for desktops and servers.
There are several versions, such as LPDDR3 and LPDDR4. A higher number indicates a newer version with better performance (in speed and/or power efficiency). For example, LPDDR4 is 50% faster and uses 40% less energy than LPDDR3. LPDDR4x uses even less power than standard LPDDR4. LPDDR5 is 50% faster than LPDDR4x.