A DNS sinkhole is a technique used in network security to redirect malicious or unwanted network traffic to a non-existent or controlled destination. It involves manipulating the Domain Name System (DNS) responses to redirect traffic from its intended destination to a sinkhole server. This can be done to block access to malicious websites, prevent communication with command-and-control servers of malware, or gather information about potential threats. The purpose of a DNS sinkhole is to protect network resources, detect and mitigate threats, and enhance overall network security.