A more thorough explanation:

Definition: A fencing patent is a type of patent that is obtained for a specific aspect of an invention that the inventor does not intend to produce but wants to prevent competitors from using in making improvements. The patent holder seeks to "fence in" any such competing improvements by making a claim whose only purpose is to protect other claims. Courts disfavor fencing claims.

Example: An inventor creates a new type of car engine that is more efficient and powerful than any other engine on the market. The inventor obtains a patent for the engine but also obtains a fencing patent for a specific aspect of the engine that he does not intend to produce but wants to prevent competitors from using in making improvements. The fencing patent protects the inventor's original patent and prevents competitors from making improvements that use the specific aspect of the engine covered by the fencing patent.

Explanation: The example illustrates how a fencing patent is used to protect an inventor's original patent and prevent competitors from making improvements that use a specific aspect of the invention covered by the fencing patent. The fencing patent is obtained for a specific aspect of the invention that the inventor does not intend to produce but wants to prevent competitors from using in making improvements. This type of patent is disfavored by courts because it can be used to unfairly limit competition and innovation.