In the context of Nostr, the term "relay" is used instead of "server" to emphasize its role in the network. A relay in Nostr is responsible for receiving, storing, and forwarding messages between users. Unlike traditional servers, which often have centralized control and can impose restrictions, relays in Nostr are decentralized and can be run by anyone. This decentralization is a key aspect of Nostr's design, aiming to create a more open and resilient communication network. So, while a relay functions similarly to a server, the term highlights its specific purpose and the decentralized nature of the network.