It would be the average fps of the port measure on the flow bench.
Chad Speier was saying and gave examples how to figure needed cfm and csa but was vague on average fps but said you should have a targeted fps from the start, I imagine most his builds are race or serious street strip. He mention you could go as high as 350 fps Pro Comp so I imagine that's all out, said 330 fps for bracket racing. He started with 310 in his example but didn't say what type of motor that would be. When using the calculations for cfm and csa seems like those heads would give a 300-310 fps. But Darin Morgan and Eric Weingartner where saying like high 200s, I've heard Darin say you need over 250 fps to keep fuel suspended. I'm assuming an average dude build is like around 300 fps but don't know for sure.