A set of colored signal lights that are used to control the flow of traffic, both vehicular and traffic. Despite suggestions by usability experts, color is the primary indicator. If you are colorblind, you may be screwed. To help this, stoplights are usually in the same order. In America, the red light is usually on top and larger. In Japan, the red light is on the left. Also, I understand in Britan, the yellow light turns on between the red and yellow cycle. In America, lights go straight to green from red.

The meaning, to [reference[ John Carpenter's Starman is this: Red: Stop
Green: Go
Yellow: Go Really, Really Fast.

The number of stoplights in a town is indicative of its size. I used to live in a two stoplight town until they took the other one out. Now, I live in a one stoplight town.

Update: They put a new stoplight in! I'm back to a two stoplight town! Woo hoo!