Side lighting is when the main light source shines on the subject from the side. This kind of lighting usually only works during the golden hours of the day, as this is the only time when the light is weak enough to still reveal detail in the shadows on the subject. Use side lighting only when there is moderate contrast between light and shadow. Strong, harsh light makes shadows black and featureless.
When the light shining on an animal comes from the side, it is best to take the photograph at the moment when the animal faces the light source. In this way, the light may accentuate the most important part of the animal (the face), often resulting in a beautiful highlight in the eye.
How you can take a similar image
Lens: Super telephoto lens.
Settings: Medium aperture. Medium ISO.
How: Wait for the moment when the animal is looking into the sun.