I dunno. Depending on the writer and their particularly axe to grind the definition can vary widely. I would like it to mean, "any fixes I needed to make were minimal and not time intensive."
Actually, I can tell; I ran split on the C source and got things like this:
disk_space.c:144:16: Only storage bin.ref_bin (type void *) derived from variable declared in this scope is not released (memory leak)
So I'm looking into a Rust version with Rustler now.
Also comes with a built-in BEAM allocator so the runtime properly reports NIF memory consumption.
the big advantage is that it will automatically box/unbox to/from c values for you and generate sane error messages (which rustler does not, last i checked) when you pass incompatible terms in to the function.
on the other hand rustler lets you precompile (which is coming in a future version of Zigler)