title: Definition of "downstream" and "upstream"
body: <p>I've started playing with Git and have come across the terms "upstream" and "downstream".  I've seen these before but never understood them fully.  What do these terms mean in the context of SCMs (<a href="https://en.wikipedia.org/wiki/Software_configuration_management" rel="noreferrer">Software Configuration Management</a> tools) and source code?</p>