Secure Digital (SD) cards are small, portable storage devices used to save and transfer data. They are commonly found in devices like cameras, smartphones, and tablets, allowing users to store photos, videos, and other files. SD cards come in various sizes and capacities, typically ranging from a few gigabytes to several terabytes. There are different types of SD cards, including SD, SDHC (Secure Digital High Capacity), and SDXC (Secure Digital eXtended Capacity). Each type has its own storage limits and compatibility requirements. SD cards are popular due to their convenience, ease of use, and ability to expand the storage of electronic devices.