SD card - Wikipedia
https://en.wikipedia.org/wiki/SD_card
Secure Digital, officially abbreviated as SD, is a proprietary non-volatile memory card format developed by the SD Association (SDA) for use in portable devices. The standard was introduced in August 1999 by joint efforts between SanDisk, Panasonic (Matsushita)...
SD Association
https://www.sdcard.org/
The SD Association has prepared multiple SD standards relating to such features as memory capacity and reading/writing speed in order for users to select the optimum card for their device. Download the SD Association Whitepapers, SD Simplified Specifications and SD Memory Card Formatter here.