The Belt of Venus is the term given to a band of usually pink or reddish color that stretches across the sky just above the dark blue band that hugs the horizon during twilight. The sky above the belt is its normal blue hue but, due to the setting or rising sun, the light reflected near the horizon takes on the reddish hue that most of the sky has when the sun is still visible for the first or last time during the day.
The Belt of Venus isn't an uncommon phenomenon. Chances are you've seen it and probably never gave much thought about it. The Belt of Venus isn't visible during every twilight period, as the cloudier the sky is, the less noticeable the belt will be. Clouds, especially near the horizon, alter the way in which light is reflected and prevent the belt from being formed. The ideal situation for seeing the Belt of Venus is a clear but dusty sky during the twilight hours. The more dust present in the sky, the more light will be reflected. The belt can be seen best facing the opposite direction of the sun (face east at dusk and west at dawn).
The Belt of Venus has also been called the antitwilight arch. The belt of dark blue-to-black coloration beneath the belt is known as the twilight wedge. The twilight wedge is the result of Earth's shadow created by the sun. The Belt of Venus is presumably named such because it appears in the portion of the sky in which Venus would be visible during the morning and evening. (I've been unable to find confirmation of this but it would make sense.)
Sources:
http://antwrp.gsfc.nasa.gov/apod/ap011209.html
http://www.weather-photography.com/Atmospheric_Optics/venus_belt.html
http://www.weather-photography.com/Atmospheric_Optics/twilight_wedge.html
http://www-2.cs.cmu.edu/afs/cs.cmu.edu/user/zhuxj/www/astronomy/atmosphere/atmosphere.html#earthshadow
and many other webpages with the same information. | 
