SD cards, or Secure Digital 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 (High Capacity), and SDXC (Extended Capacity), each designed for specific storage needs. They are easy to use; simply insert the card into a compatible device, and it can be accessed like any other storage medium.