A service mesh is a dedicated infrastructure layer that manages communication between microservices in a cloud-native application. It provides features like load balancing, service discovery, and security, allowing developers to focus on building applications without worrying about the complexities of service interactions. By using a service mesh, organizations can improve the reliability and observability of their services. It typically includes components like a data plane for handling traffic and a control plane for managing policies and configurations, ensuring that services can communicate efficiently and securely across different environments.