What is Density Altitude? I'm trying to get a deep understanding of the term: Density Altitude. 

So I have read the explanations in my instruction book, and online articles. 
One source explained it differently then the other which confused me. 

Wikipedia defines Density Altitude as: 


  The density altitude is the altitude relative to standard atmospheric
  conditions at which the air density would be equal to the indicated
  air density at the place of observation. In other words, the density
  altitude is the air density given as a height above mean sea level..".


https://en.wikipedia.org/wiki/Density_altitude 

So if I would believe Wikipedia then I could look at the ISA table to find the altitude by using the pressure. 

Here is an ISA table:



My instruction book (Aerodynamica, prestatieleer en vliegtuigtechniek by Bas Vrijhof on page 112, written in Dutch) claims this: 


  in de ISA is de dichtheidshoogte altijd gelijk aan de drukhoogte


Translated to English: in the ISA the density altitude is equal to the pressure altitude.

So, let's say I'm flying in an aircraft, the pressure is "22.22 Hg", and the outside air temperature is -0.9°C. The altitude in the ISA would be 8000 ft. The Density Altitude would also be 8000 ft.

Skybrary defines Density Altitude as: 


  Density altitude is pressure altitude corrected for temperature.


Link: https://www.skybrary.aero/index.php/Density_Altitude

This explanation contradicts with the Wikipedia explanation: 


  the air density would be equal to the indicated air density at the
  place of observation


On another wikipedia article I found this: 


  De relatie tussen temperatuur, hoogte en luchtdichtheid kan worden
  uitgedrukt in density altitude. 


Translated to English: 
The relationship between temperature, altitude and air density can be represented as density altitude.
Link: https://nl.wikipedia.org/wiki/Opstijgen#Benodigde_snelheid

So in short, each source explains Density Altitude in their own manner, some contradict the other which confuse me.

So my question is: 

What is Density Altitude?
The concept of 'density altitude' is kind of like the concept of 'wind chill'.
Stick with me here, I'm going somewhere with this.
Cold weather is dangerous for the human body, and wind (because of increased heat loss on human skin) makes it worse. But how much worse? Is it worse to be outside in -10C temperatures with a 20 knot wind, or -15C temperatures with a 12 knot wind? The concept of 'wind chill' resolves those two values into a single easy number.
Density altitude works the same way. It's difficult and tedious to compare and contrast how an airplane will perform on a 25C day with a pressure of 29.80 at an elevation of 600 MSL, versus a 20C day with a pressure of 30.17 at an elevation of 1250 MSL. We need a way to mash all of these variables into one easy-to-use number. That number is density altitude.
So just as I can say &quot;The wind chill is -10C&quot; and it doesn't matter whether it's warm but windy or cold and calm, I can say &quot;The density altitude is 2,000&quot; and everyone will have the same idea of the expected performance of the airplane, no matter what combination of factors led to that result.
Once you start thinking of (and using!) density altitude as a simplification tool, its value becomes a lot more obvious.