Take a look at these examples of silhouettes.
Silhouette photography is when your subject is back lit, which is exactly what it sounds like. The light is behind it and there's little to no light in front of it. Think of it this way. You'll be pointing your camera directly at the light, and whatever is in front of that light will appear as a silhouette (a dark outline of it's shape).
When you're choosing something to shoot in silhouette, make sure your subject has a shape that will pop when it is back lit. I would really suggest shooting your silhouette at sunset for the best effect. Check out Longshore Park off of Plum Canyon! There's a great hill that will provide a perfect spot for a back lit photograph at sunset! But you don't only have to shoot on hills or in picturesque locations. Take a look around at about 5:30 pm, when the sun goes down. The lighting will be perfect for you to find a great silhouette to shoot.
Send your pictures to firstname.lastname@example.org
by Saturday, 27th at 12 pm. Good luck!