XQD is a type of high-speed, high-capacity memory card designed for use in professional-grade digital cameras and other devices that require fast data transfer and large storage capacity. XQD cards are based on the PCI Express (PCIe) interface, which is a high-speed computer bus that is commonly used to connect peripheral devices to a computer. XQD cards are designed to be used with devices that have an XQD card slot, and are typically faster and have a higher capacity than other types of memory cards. They are often used in professional-grade cameras and other high-performance devices where fast data transfer and large storage capacity are critical.