Back lighting is when the light shines directly towards the photographer from behind the subject. A good back-lit image is one where you can see all the detail in the subject despite the light only coming from behind and not shining directly on it.
Only try back lighting if you don’t have any other choice. Using back lighting under the wrong light conditions (when the light is too harsh) is a common mistake among beginners. Try whenever possible to use front lighting.
The only condition when back lighting will work is during the first and last few minutes of the day when the contrast between light and shadow is very low. Be very careful of flare. Prevent the sun shining on the front element of the lens.
How you can take a similar image
Lens: Telephoto lens.
Settings: Maximum aperture. Low ISO.
How: Use a lens hood on your lens to minimize flare. The front element of your lens must be clean, as a dusty lens will pick up more flare than a clean one.