binfmt is a kernel module that magically allows the kernel to figure out
an interpreter for any given binary. qemu-static can use it to
transparently run foreign architecture binaries against the kernel.
specifically this for example allows running an arm container on amd64.
alas, the way it is configured in 18.04 is kaput and actually prevents it
from working in certain cases (notably flatpak/bubblewrap).
fixed for 20.04 already