What term refers to a computer or program that manages access to a centralized resource in a network?

The correct term that denotes a computer or program managing access to a centralized resource in a network is "Server." A server is specifically designed to provide services, manage requests, and handle multiple users accessing resources such as files, applications, or websites simultaneously. It acts as a central point in a network, allowing clients—devices or programs requesting resources—to communicate and receive data effectively.

In the context of networking, clients are individual devices that request services from the server, while routers are responsible for directing data packets between networks, and switches connect devices within a local area network (LAN) to facilitate communication. However, none of these perform the specific function of managing access to centralized resources like a server does, which is why "Server" is the most appropriate answer.