Subversion is used to keep track of the changes made to the Wireshark source code. The Wireshark source code is stored inside Wireshark project's Subversion repository located at a server at the wireshark.org domain.

To quote the Subversion book about "What is Subversion?":

“Subversion is a free/open-source version control system. That is, Subversion manages files and directories over time. A tree of files is placed into a central repository. The repository is much like an ordinary file server, except that it remembers every change ever made to your files and directories. This allows you to recover older versions of your data, or examine the history of how your data changed. In this regard, many people think of a version control system as a sort of "time machine". ”

	Tip: Subversion and SVN is the same!
	Subversion is often abbreviated as SVN, as the command-line tools are abbreviated that way. You will find both terms with the same meaning in this book, in mailing list discussions and elsewhere.

Using Wireshark's Subversion repository you can:

Subversion is divided into a client and a server part. Thanks to Gerald Combs (the maintainer of the Subversion server), no user has to deal with the maintenance of the Subversion server. You will only need a Subversion client, which is available as both a command-line and a GUI tool for many different platforms.

For further reference about Subversion, have a look at the homepage of the Subversion project: https://subversion.tigris.org/. There is a good and free book about it available at: https://svnbook.red-bean.com/.

Please note that Wireshark's public (anonymous) Subversion repository is separate from the main repository. It may take several minutes for committed changes to appear in the public repository - so please be patient for a few minutes if you desperately need a code change that was committed to the repository very recently.