In the film days, the "normal" lens for a 35mm camera was a 50mm lens.
If you bought a camera kit (body + lens), the lens was a 50mm lens.
So the vast majority of the public had and used the 50mm lens. Hence its familiarity and the catchy name.
BUT that was a 35mm film camera.
Today with digital, that 35mm film is equivalent to the "full frame" cameras.
As was mentioned, the APS-C camera is a crop camera, so the calculated equivalent of the 50mm lens is about 31mm (50mm/1.6crop), which does not exist. So you get the closest lens to that, which is 35mm, and call it done. That is your APS-C equivalent to the nifty-fify.
Having said that, Canon does not make a 35mm crop lens (that I know of). If you want a 35mm lens for your Canon, you have to buy either a full frame Canon lens ($550), or a Youngnuo crop lens ($100).
The 'nifty-fifty' is not as versatile as you may think it is.
It is a SINGLE focal length lens, a prime lens. And that has limits.
You have to use your feet, to compensate for the fixed focal length.
- If the subject is too small, you use your feet to move you closer, to get a larger image.
- If the subject is too big, you use your feet to move you farther away, to get a smaller image.
- But what if you can't get closer?
- Then you switch to a telephoto lens.
- But what if you can't back up enough?
- Then you switch to a wide angle lens.
With your zoom, you just twist the zoom ring, and the lens changes the viewing angle.
Is this a big deal? Maybe, maybe not.
People have used fixed lens cameras for decades, before zooms were invented.
Then with film SLRs, swapping/changing lenses was a fact of life. This meant having multiple lenses; wide, normal and tele.
We adapted to what we had, and used it.
What the 50 and many primes gives you is a FASTER lens.
In practical terms, this means that you can shoot in lower light than with your zoom.
Example, when I shoot basketball in my local gym, I switch from my slow zoom to the fast 35mm f/1.8 lens. I loose the zoom function, but I gain in the lower light capability.