microSD (also called TransFlash) is a smaller variant of Secure Digital (SD), created by SanDisk and introduced in 2005.
SanDisk introduced microSD as current memory cards were too large for newer mobile phones.
Initially, microSD cards were available in capacities of 32, 64, and 128 MB, but the original microSD standard allowed for up to 2 GB of storage. microSDHC (introduced in 2006) allows for between 4 and 32 GB, and microSDXC (introduced in 2009) allows for up to 2 TB. As of May 2014, that largest commonly available microSDXC cards are 64 GB.
microSD cards will work in devices that require SD or miniSD cards by use of an adaptor.