I chose this photo because it is easy to describe Rim Lighting.
When the sun is positioned behind the subject when you take a picture the lighting is referred to as backlighting. If the sun is in such a position to highlight the edges of the subject, in this case the model's hair, it's known as rim lighting.
Rim lighting is a great method used to outline the subject and produce a striking effect that shows shape. It works best when the edges of the subject are thin so that you get the light bursting through, creating a wonderful highlighted outline. This thin highlight helps create a separation between the subject and background. In the case of the photo above, it accentuates the messiness of the hair, which I believe is intentional.
When you are at your photo shoot, ask the model to turn slowly around and look for the outline around the edge of the model. As soon as you see it, ask the model to stop turning. Remember to meter with the light sensor facing the camera and hold it in front of the model's face.
Photo by SheLeftOnTheNightTrain