Tempo is a pretty fast pace (but not your fastest), for me it's somewhere around 4:15/km. By steady pace, I just mean something that's still pretty quick but relatively comfortable over longer distances, around 4:30/km ish. There's a handy tool on Strava that shows me my Pace Distributions based on my fastest race times, but I'm a lot fitter than I actually thought I was (hopefully I'll be able to show that tomorrow at Parkrun as I'm aiming for a sub-19 minute 5k).

When I refer to an inverted pyramid, it just means that I set out at my peak paces, purposefully slowed down in the middle of the run, and then sped up in the latter stages. I often do pyramid workouts (which is just the opposite), but with two segments at peak paces, I find inverted pyramids are more challenging and offer a better workout.

You can sort of see what I mean from this chart...