tr.v. back·light·ed or back·lit (-lt), back·light·ingback·lights

To light from behind:

This is one of my favorite lighting techniques.  As you can tell from the definition above it is a really simple lighting technique.  All you have to do is put your light source behind your subject. Even at high noon (when the sun is supposedly directly overhead) backlighting is an option.  I use backlighting about 80% of the time.  The other 20% is mainly spent shooting in the shade.  There are a few things to remember when Backlighting your subject outdoors:

1. Expose for your subject not the background.

If you are taking a portrait then you should prioritize the person and not the background.  If you expose for the background your subject's face will be super dark. In my opinion it is okay to somewhat "blow out" the background when you are taking portraits of people.  This is a great time to use spot metering so you can expose on for the subjects face.

2. Consider using a Long Lens with a lens hood

The later in the day you are shooting the higher risk you run of lens flare.  If you are backlighting, you are shooting into the sun, and the lower the sun is the more it will be shining into your lens.  Using a long lens with a lens hood helps you better manage/reduce the amount of sun coming into the lens.

3. Move around

Even though your light source is behind the subject, is doesn't mean that you have to all be aligned.  What I mean dont' have to have the Sun directly behind your subject and shoot from directly in front of your subject.  Move to the side until you are happy with your composition and amount of lens flare.

Here are some examples of BackLighting: