Which best defines a "replica set" in MongoDB?

A "replica set" in MongoDB is best defined as a group of servers that maintain the same data, which is crucial for ensuring high availability and redundancy. In a replica set, one server acts as the primary node while the others serve as secondary nodes. The primary node is responsible for receiving all write operations, and the data changes are then replicated to the secondary nodes. This architecture allows for automatic failover; if the primary node goes down, one of the secondary nodes can be elected as the new primary, ensuring that the database remains operational and accessible.

This approach enables fault tolerance and increases data availability, as the secondary nodes can also be utilized to handle read operations, thereby distributing the load and improving performance. Moreover, in case of maintenance on the primary server or unexpected outages, the system can quickly recover without significant downtime, which is vital for mission-critical applications.