A service mesh is a dedicated infrastructure layer that you can add to your applications to provide capabilities like observability, traffic management, and security, without adding them to your own code. A service mesh consists of network proxies paired with each service in an application and a set of management processes. The proxies are called the data plane and the management processes are called the control plane. The data plane intercepts calls between different services and processes them; the control plane is the brain of the mesh that configures and monitors the data plane1. A service mesh makes communication between applications possible, structured, and observable by providing features such as load balancing, service discovery, encryption, authentication, authorization, routing, retries, timeouts, fault injection, metrics, logs, and traces2.
The other options are incorrect because:
Provides dynamic application load balancing and autoscaling across multiple clusters and multiple sites is a description of VMware Tanzu Service Mesh Global Namespaces feature3, which is built on top of a service mesh. It is not the purpose of a service mesh in general.
Provides a centralized, global routing table to simplify and optimize traffic management is a description of VMware Tanzu Service Mesh Global Mesh Network feature4, which is also built on top of a service mesh. It is not the purpose of a service mesh in general.
Provides service discovery across multiple clusters is a partial description of a service mesh, but it does not capture the full scope of its purpose. Service discovery is one of the features that a service mesh provides, but it is not the only one.
References: What’s a service mesh?, The Istio service mesh, Service mesh - Wikipedia
