RxJava is an asynchronous data stream programming tool that can also be used as a Java CSV reader. It's useful for event-based programming where you can observe and react to changes in the stream of data. In this example, RxJava is used to load CSV data into Couchbase by transforming it into JSON documents that can be stored in the NoSQL database. The process involves creating a CSVReader object, connecting to the Couchbase server, mapping the CSV data into JSON documents, and upserting them into the database using an Observable. This approach allows for reactive programming and efficient processing of large datasets.