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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 Erlang? Is there a definitive reason to use one term over the other?
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.
Asked Earlier in Stack Overflow : What is the difference between a process and a thread?
Really interesting question! For a (slightly sloppy) one line answer: a process can manage a number of threads (multiple threads to a process). See: https://msdn.microsoft.com/en-us/library/windows/desktop/ms684841(v=vs.85).aspx
The actual differences in memory allocation and access are best described here (multiple threads share a memory space, the process they belong to): What is the difference between a process and a thread?
The wikipedia visual (and subsequent discussion about thread scheduling) provide a pretty good grounding. If you are more interested in more of the technicalities, consider reading the Silberschatz OS textbook!
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