Confused about types of storage and encryption

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I'm confused here. The naming of type of storage. There is SD and External SD and "device". I assume SD is the internal (16GB) memory and External is the (64GB) Micro SD card I have inserted?

With that in mind, I get confused on file managers that say SD memory because that makes me think Micro SD card. They even show it as as a card icon in OI File Manager! But now I realize that exSdCard is my microSD.

So now my question is the encrypting. We have two options:

Encrypt Device and Encrypt SD card

This is confusing! Is the "device" the internal 16GB SD?
Or is SD the internal memory and Device is some other internal section?

Is there no option to actually encrypt my 64GB micro SDcard?

Halp

Device=accounts, settings, downloaded apps & their data, media if stored on internal, and some other files all stored on internal phone memory.