If they are talking about HP and Torque they probably mean the power you make aside from your peak power.
If you look at a dyno graph of a supra that makes like 1500hp its gonna make no power until all of a sudden when the turbo finally spools up, this has a high peak power but nothing "under the curve". You can modify an engine and end up with the same peak HP but have more power "under the curve" and the latter will be faster
im not very good at explaining things, hope this helps
With cams, picture the lobe. For any given duration and lift, there is a curve. If you plot the valve events over time on a graph you would see a bell-shaped curve starting with the valve opening, then reaching peak lift, then dropping down to close. When you grind a cam you can make the lift ramps faster. So, the graph would look the same at the beginning and the end, but the lines would rise and fall more sharply.
The same happens for torque and HP peaks. If you have two engines, both with identical HP and TQ peaks but one has broader curves on the dyno, there is more area "under the curve." Consider this graph in the picture below. They both start and end at 0 and they both peak at 29, but the pink line shows more area "under the curve."
In general, most cams that provide more lift under the curve will provide more power and torque under the curve. If you have two engines with identical peaks but one has more area under the curve, the engine with the broader curves will be faster. As you are accelerating through the RPM range, the broader-curved engine will supply more torque and HP at more points along the way and therefore be faster.