I'm looking at:-
https://elinux.org/Beagleboard:BeagleBoneBlack_Debian#2018-03-25_-Debian_9.28Stretch.29_-_Weekly
... and trying to decide which image I want to use.
So I presume the ones headed 'microSD/Standalone' are the ones that boot
and run from the microSD card and the 'Flasher' ones are the ones that
copy themselves to the eMMC at boot.
Then there are 2Gb and 4Gb, I can understand that bit! 
Finally there are lxqt, lxqt-xm, iot and console. Again I *think* I
understand these as the GUI (lxqt, lxqt-xm) or not (console). What
does 'iot' mean though.
I don't need a GUI so I can go for the "microSD/Standalone:
(stretch-console) (All BeagleBone Variants & PocketBeagle)" image.
This will presumably simply boot from and use the microSD card.