Rim and Kicker lighting?
Rim lighting is the effect of using light on the the extreme outer edges of a subject while kicker lighting adds light and shadow to surfaces to the edge of your image. Depending on the position of a light source a light can be termed a rim, kicker or combination rim and kicker light. Rim and kicker light sources come from behind a subject and depending on angle will give different effects. During the day, close to sunset or sunrise, the sun can be used as a kicker or rim light depending on where you place your subject. The sun does not have to be your only light source and using a strobe (or flash unit) can add a secondary rim or kick to the opposite side of an image. In the image example below I used the sun to the right of the image and a strobe to the left of the image to create a combination kick and rim effect.
Using kicker or rim lighting without fill lighting produces silhouette or semi-silhouette images. In the sample below I needed a rim light, but since the sun had just set I could not get that rim glow from the sun, so I added a strobe behind the couple. The strobe was pointed slightly down to also add light to their immediate background.