The tendency for fear of transgressing some law to keep people from engaging in legal behaviors. For example, if the speed limit were 55 miles per hour, and the punishment for exceeding it were that a sensor in your speedometer would instantly detonate a bomb, driving your engine block through your sinuses at roughly the speed of sound, you would probably give yourself a good 15 mph cushion so that a moment's lapse of attention didn't result in your untimely death. Driving 50 would be legal, but hardly anyone would do it due to the chilling effect.

The chilling effect also crops up in discussions of obscenity statutes. In this case the effect is caused by the vague definition of "obscenity" (typically something along the lines of: "I can't define it, but I know it when I see it"). The chilling effect of strict obscenity statutes can prevent people from publishing material that is not obscene, but merely controversial because of the uncertainty in what, exactly, is or is not obscene.