Yes, that's how it feels to get techno-babbled!
Of course I could try to explain a little bit what all this is about:
A "class" is a notion from object oriented programming, a class is a piece of code that bundles both a state and methods to change it. A "rational number" for example would be represented by a class in Java that has both a state (the value of the number) and methods like "multiply by an integet i".
"checked into trunk": a "versioning system" is a software program that helps you to manage changes to files, by giving each file a version number. When you change the file locally on your computer, you can check the change file into the trunk, which means you tell the versioning system "here is a new version of this file". The versioning system then increases the version number of this file and provides means to find out what has changed. Instiki provides this service, too: you can see changes by clicking on "changes" at the bottom of the page. The versioning system used by the azimuth code project is called "subversion" or "SVN" for short.
The "trunk" is the main "branch" and the "head" or "head version" referes to the newest version on a branch. If you write a paper and develop a line of thought that you are not sure if you would like to include it, you could maintain two versions of your paper: One with the worked out stuff on the "trunk", and one with this different line of thought on a "branch". Then you can work on and change the version on the trunk and on the branch independently. Maybe a month later you find out that you would like to include certain parts of the branch into your paper, you can then "merge" these changes from the branch to the head in the trunk, and abandon the branch.
If you fixed a bug on a branch of a software and transfer it to the main version, you would therefore say: I merged the bug (fix) into the head of the trunk.
(No, really, that's what people say).