<p>What is the technical difference between a process and a thread?</p>

<p>I get the feeling a word like 'process' is overused and there are also hardware and software threads. How about light-weight processes in languages like <a href="http://en.wikipedia.org/wiki/Erlang_%28programming_language%29" rel="noreferrer">Erlang</a>? Is there a definitive reason to use one term over the other?</p>

Both processes and threads are independent sequences of execution. The typical difference is that threads (of the same process) run in a shared memory space, while processes run in separate memory spaces.
I'm not sure what "hardware" vs "software" threads you might be referring to. Threads are an operating environment feature, rather than a CPU feature (though the CPU typically has operations that make threads efficient).
Erlang uses the term "process" because it does not expose a shared-memory multiprogramming model. Calling them "threads" would imply that they have shared memory.