Make's output, the number in the brackets

Question

What's the significance of the number in the square brackets in Make's output?

make[7]: Leaving directory '/home/mike/...'
make[6]: Leaving directory '/home/mike/...'
make[6]: Entering directory '/home/mike/...'

Is make multi threaded and this is the thread's number, or is it the level of makefile traversal, or what exactly? It's larger numbers on my big projects, but on my personal ones (with just a few source files) it's typically make[1] so I assume it has to do with the complexity.

I can't seem to find this in the documentation.

Answer 1

Make has the ability to call other makefile within itself. The number in the brackets is the number of makefile called from your root makefile.