miniSDHC is a version of the miniSD flash memory storage card that has the same form factor but provides higher capacities. A standard miniSD card will work fine in a slot compatible with miniSDHC, but a miniSDHC card won't be recognized by incompatible hardware. Not all portable devices that are sold now with support for the miniSD storage format are compatible with the miniSDHD variety. miniSDHC offers capacities up to about 8GB.
There are a variety of Secure Digital (SD) products available..
Secure Digital (SD) --> Original SD card offering capacities up to 8GB currently.
miniSD --> A smaller form-factor version of the original SD card.
microSD --> Currently the smallest flash memory card on the market.
miniSDHC --> High Capacity version of miniSD card.
microSDHC --> High Capacity version of microSD card.
SD plus --> A form of SD card developed by SanDisk.with USB additions.
Eye-Fi --> An SD card with built in Wifi capabilities of its own.
Gruvi --> A form of SD card developed for content distribution by SanDisk.