When someone says "I run 60, 70, 80, 100" mpw, is that an average or the peak?

It should mean that's what they run on average every week, not what they run during a peak week of training. But people tend to fudge their mileage all the time.

I just did 84 miles in 5 days, including 75 miles the first 4 days, but my average weekly mileage is around 70ish, if you look at the long term. I only do really high mileage like that for 3-5 days, and cycle it into my training about once every 20-30 days.

I think you get diminishing returns from sustained high mileage, but you get a good boost from sustained high mileage by about the 4th day.

I have 2 running cycles a year. 1)Mid-June through late November. then i take a week or 2 off, and run mid-December though early June. take another 1 or 2 weeks off and it starts over again.

I usually say my current average at that point in the cycle. For example, as of today I have ran 390 miles since December 7th, which works out to about 46.2 miles/week. So if asked I would probably say I run 45 miles a week, but sometimes a little more (since 3 of those weeks have been 49-55 miles).