Secure Digital, officially abbreviated as SD, is a proprietary, non-volatile, flash memory card format the SD Association developed for use in portable devices. The standard was introduced in August …Secure Digital, officially abbreviated as SD, is a proprietary, non-volatile, flash memory card format the SD Association developed for use in portable devices. The standard was introduced in August 1999 by SanDisk, Panasonic and Toshiba as an improvement on MultiMediaCards. SDs have become an industry standard. The three companies formed SD-3C, LLC, a company that licenses and enforces intellectual property rights associated with SD memory cards and SD host-and-ancillary products.