"π" is a federally registered trademark, so in the strictest sense, a π Speaker is one that either we've sold or licensed. The kits are a collection of parts, and we've essentially licensed the builder to build one speaker with them. There are probably some technicalities that I've oversimplified, but you get the idea.Like Bill said, I've always sort of considered any speaker built around the ideas found in the "Pi Alignment" paper to be a π Speaker. There have been some other configurations I've done that I'm proud of and that aren't in that paper, like the new eight π loudspeaker. There are also other documents you'll find here that describe ideas integral to most π Speakers too, like crossover designs and what-not.
So really, in my mind, a π Speaker is one of a handful of loudspeaker configurations that are commonly discussed here. It's a style or design type based on procedures outlined in the documents posted on the π Speakers website and discussion forum. But in the truest sense, a π Speaker is one that we've built or licensed to be built using information provided here.