Bitcoin is, among many things, a software system with many participants running Bitcoin software and who all connect to each other over the internet forming a Bitcoin network. It's a live system yet the software that runs it is continuously under development. This is what the Bitcoin Core dev team does, and sometimes they allow other people to participate in development like an open source project. There are other developers who also develop other Bitcoin code which fulfills the same purposes. Then all of the various Bitcoin nodes run a version of the software.
Of course, any...