Somewhere it should be lore that the person that named these syscalls went on to name functions in PHP.
It's not obvious in modern editors or code browsers, but the Linux kernel, much (most?) of the base Linux user land, and the various *BSD projects (kernel and user land) still use hard tabs for indentation.
I am asking because I tried to write to basic nasm programs in order to learn and I used the c preprocessor (cpp) over my nasm files to take advantage of the libc macros from <sys/syscall.h> and they were all of the form __NR_syscall
Then the other responses' assumption, "NumbeR", seems correct
[0]: https://github.com/torvalds/linux/blob/master/Documentation/...