Sure. The vertical axis is loudness, in decibels (dB). The horizontal axis is frequency, in hertz (Hz).
The green lines are the compensated frequency responses of the headphones indicated, the yellow, grey, and purple lines are the harmonic distortion levels for 2nd order, 3rd order, and 4th order respectively. The distortion loudness levels are relative to the frequency response loudnesses at any frequency point.
In terms of frequencies and their corresponding descriptions, our hearing / most music is between 20 Hz and 20000 (20k) Hz. Within that range, 20-50 Hz or so is sub-bass, 50-300 Hz or so is bass (with mid-bass centered at 150 Hz or so), 300-750 Hz or so is lower midrange, 750-2500 Hz or so is central midrange, 2500-4000 Hz or so is upper midrange, 4000-7500 Hz or so is lower treble, 7500-12000 (12k) Hz or so is central midrange, and 12kHz - 20kHz is upper treble ~ supersonic.
The most important aspect of an ideal measured response is evenness. By that I mean lack of major bumps, peaks, valleys, spikes, humps, jaggeds, and such. Now there are exceptions to this but it typically holds true. A very even response will to our ears sound very coherent and smooth, nothing will sound lacking or too much.
Past that aspect, other traits to look for are 'good' (and this is somewhat subjective) tonal balance, and overall low harmonic distortions (another somewhat subjective point).
For me, an ideal tonal balance is flatness from lowest frequencies all the way up to central midrange, relatively relaxed upper mids / lower treble, small hump at mid-treble, and present but somewhat rolled off upper treble. This allows for a rich, engaging sound that isn't too forward/aggressive, or tizzy/fatiguing, yet has the sparkle needed to bring out the liveliness in music. Luckily the modded HE500s, as you can see, gets that just right. And it's no surprise, I specifically devised and updated the earpad mod over the last 9 months or so to subjectively mold it to my ideal sound signature, turns out it's dead on in measurements.
Thanks, you just sold me a HE-500.