I know nothing about the mathematics. But I think it&#x27;s fair to say that in general people tend think of particles as being a _stable_ unit of some sort. So the term &quot;particle&quot; becomes less appropriate the less stable something is, and time is often a factor when thinking about stability.<p>If someone were simply to slam 4 neutrons together, for how long would they need to stay together for this to be deemed a real particle? I think it&#x27;s for this reason the original commenter quoted the use of the term &quot;particle&quot;.