UBS Mini B was once the standard for USB devices, especially certain game controllers, but what exactly was the Mini B standard meant for?

My friend has a 7D, and the SD card reader on her computer has crapped out (we think). She doesn't have the official IFC-200U/IFC-500U interface cable that came with the camera, but for purposes ...

Although USB has set standards, you can find some odd cables and ports out there. So, why do some USB connectors have small lightning bolts on them? ... like Mini USB, Micro USB, USB Type-B, ...