For those of us that are ignorant, can somebody tell me what a PULL request in layman's terms is? And what is it used for?
Since the project is open source, anyone can change the files. However, this creates a "fork", their version of the software is different from everyone else's. This means that they need to incorporate any future changes into their fork.
A pull request allows them to submit the change back to the main project. If it is accepted, the changes become part of the official version of the software.