Istio is an open-source service mesh platform that provides a comprehensive solution for managing, securing, and monitoring microservices in a distributed system. It acts as a middle layer between services, handling communication, routing, and load balancing, as well as providing visibility into the traffic flowing between services. Istio also offers advanced security features such as access control, authentication, and encryption to ensure that communication between services is secure. By centralizing these functionalities, Istio simplifies the complexity of managing a microservices architecture and allows developers to focus on building and deploying their applications without having to worry about the underlying infrastructure.