An SD card, or Secure Digital card, is a small, portable storage device used to save and transfer data. Commonly found in devices like cameras, smartphones, and tablets, SD cards come in various sizes and storage capacities, ranging from a few megabytes to several terabytes. They are designed to be easily inserted and removed, allowing users to expand their device's storage or transfer files between devices. SD cards are available in different formats, including microSD, miniSD, and standard sizes, each suited for specific devices. They use flash memory technology, which means they retain data even when not powered. This makes them a reliable option for storing photos, videos, music, and other digital files.