Interesting; since as far as I can tell, Tyler Cowen and Patrick Collison use definition #2 in the now-famous Atlantic article: "In an era where funding for good projects can be hard to come by, or is even endangered, we must affirmatively make the case for the study of how to improve human well-being."

Maybe PS adopted definition #1 instead to avoid seeming redundant compared to EA?

Do you think defining 'progress' is an important part of the agenda? Or is it more of a distraction?

Far as I can tell, there are 3 different potential definitions for progress:

1. Essentially just technological/scientific progress
2. Some consequentialist-ish idea like "people are happier/wealthier"
3. Any change in society or technology which is not a reversion to something that has been done before

Options #1 and especially #2 leave fairly little room for discussion on whether or not any specific instance of progress is a good thing, while option #3 is much more morally neutral, but perhaps not what people have in mind when they think of 'progress'.