It's a Makefile[1]. They are quite simple really. They're defined like this:

  target: dependencies
      command

The command is run by a shell (e.g. bash!) when the target is called to be run. For example...

  all: hello world
      echo "!"

  hello:
      echo "Hello"

  world:
      echo "World"

Now if you run "make", you will see each command being run. By default, if you call "make" with no arguments, the "all" target will be run. You can also call "make world" for example, to have it only run the "world" target. As you can see, first the dependencies of the target are called, then the command of the target is run.

It's often used by C/C++ projects in order to manage dependencies, but can be used for anything really.

Here's a short tutorial you can walk through if you're interested in how it works and why it's useful: http://mrbook.org/blog/tutorials/make/

1. https://en.wikipedia.org/wiki/Makefile