What is Chilling Effect?

Legal Definition
In a legal context, a chilling effect is the inhibition or discouragement of the legitimate exercise of natural and legal rights by the threat of legal sanction. The right that is most often described as being suppressed by a chilling effect is the US constitutional right to free speech. A chilling effect may be caused by legal actions such as the passing of a law, the decision of a court, or the threat of a lawsuit; any legal action that would cause people to hesitate to exercise a legitimate right (freedom of speech or otherwise) for fear of legal repercussions. When that fear is brought about by the threat of a libel lawsuit, it is called libel chill. A lawsuit initiated specifically for the purpose of creating a chilling effect may be called a Strategic Lawsuit Against Public Participation, or more commonly, a "SLAPP suit".

"Chilling" in this context normally implies an undesirable slowing. Outside of the legal context in common usage; any coercion or threat of coercion (or other unpleasantries) can have a chilling effect on a group of people regarding a specific behavior, and often can be statistically measured or be plainly observed. For example, the news headline "Flood insurance [price] spikes have chilling effect on some home sales," and the abstract title of a two‐part survey of 160 college students involved in dating relationships: "The chilling effect of aggressive potential on the expression of complaints in intimate relationships."
-- Wikipedia
Legal Definition
Cooling the earth's surface temperature by unclouded sky at night or increased number of particles in the upper atmosphere that block sunlight. Contrasts versus greenhouse effect.