I am a quite new Linux user and stumbled upon something that I don't understand. I just bought a new 16GB card, installed Raspbian onto it, and expanded the filesystem. According to the output of df -BM, the root filesystem's size is 14895M, of which 1509M is used and 12763M is available.
I understand that 16 GB = 14,83 GiB, but still, 12763M + 1509M = 14272M, so 623M is missing. What happened with that "missing" space?