A private subnet is a segment of a computer network that is not directly accessible from the public internet. It is used to enhance security by isolating sensitive resources, such as databases or application servers, from external threats. Devices within a private subnet can communicate with each other, but they require a network address translation (NAT) gateway or similar service to access the internet. In cloud computing environments, such as those provided by Amazon Web Services (AWS) or Microsoft Azure, private subnets are commonly used to host backend services. This setup allows organizations to control access to their resources while still enabling necessary internet connectivity through secure channels.