I've been looking at Micro SD memory cards and had no idea what the difference was between them. I thought I'd post up some details for anyone looking at purchasing their first, or next Micro SD card, hope it helps.
HC - high capacity
XC - eXtended capacity
Micro SD is 2 GB and below.
Micro SD - HC is between 4 and 32 GB.
Micro SD - XC is 32 GB to 2 TB
Here's an article on the future 2TB Micro SD - XC, as of now the highest capacity is 256GB
http://www.micro-sdxc.com/
The micro SD - HC also has classifications relating to its data transfer rate

Class 2 - 2MB/sec. minimum data transfer rate

Class 4- 4MB/sec. minimum data transfer rate

Class 6- 6MB/sec. minimum data transfer rate

Class 10 - 10MB/sec. minimum data transfer rate
UHS - Ultra high speed
UHS 1 - 10 MB/s
UHS 3 - 30 MB/s
What are the applications for Speed Class?
Class 2 : H.264 video recording, MPEG-4, MPEG-2 video recording
Class 4: MEPG-2 (HDTV) video recording, DSC consecutive shooting
Class 6: Mega-pixel DSC consecutive shooting, professional video camera
Class 10 ; Full HD Video Recording, HD Still Image Continuous Shooting
UHS 1 ; Full HD Video Recording, HD Still Image Continuous Shooting
UHS 3 ; 4K/2K Video Recording
From The SD Association
https://www.sdcard.org/consumers/speed/speed_class/index.html
Micro SD Cards are also backward compatible with SD card devices. by using an appropriate adapter.