This question came up on the forum, I thought I would answer it here to a wider audience.
This project ran for a couple months with no name. In fact, the FreeBSD jail that runs our CVS is still called “projectx”.
Scott and I were the only two members of the project at the time, as the founders. We ran through numerous possibilities, with the main difficulty being finding something with domains available. Scott came up with pfSense, pf being the packet filtering software used, as in making sense of pf. My response was less than enthusiastic. But, after a couple weeks and still having nothing better, we went with it. It was even said “eh, we can always change it.”
Others have suggested it stands for things including Plain F…. Sense, but I won’t go there.
I started a thread on the private developers list sometime last year proposing changing the name of the project. Most people didn’t care one way or the other. A couple said they thought pfSense was fine. There wasn’t any serious interest in changing. We had some extensive lists of options put together, but never really came up with anything compelling enough to change.
Got an idea for a replacement name with domains available? Email me. Think the name is fine as it is? Think we should change? Feel free to leave comments or email me. I don’t think a name change is very likely, but thought I would mention it.
Update: From numerous emails and the comments here, the opinion of the vast majority seems to be “keep the name!” I’m glad our user base thinks it’s good, I’m certainly satisfied with it then.