As more and more people start using and discovering Pants, we've discovered that it's difficult to talk about the tool without introducing it as The Pants Build System, which isn't very snappy or easy to remember. Especially in titles of posts or in tweets without that much context, "Pants" on its own doesn't make a lot of sense to many people, and if you don't explicitly append "build", it's also really difficult to search for "Pants".
Over the years, our online presence has sprung up around the name Pantsbuild. We use Pantsbuild as our Twitter handle, the project's username on Reddit, our domain name, and our GitHub organization name, to point out just a few. There's more than a few articles from people in the community (but not affiliated with the project) that talk about "using Pantsbuild".
After some discussion amongst maintainers and on the Pants Build community Slack, we've decided that Pantsbuild is a perfectly fine thing to call the project too. This doesn't mean that Pants is no longer the name of the project, it's just that Pantsbuild is a name that you can use if you feel like Pants constrains your expression.
So, if you see us talking about Pantsbuild, that's why. Now you can say Pantsbuild too.