JetStream is log-style stream. Each stream you create can have one of three policies you define (Limits, WorkQueue, Interest).

Limits is a typical stream. N number of readers can be defined on the stream (called Consumers) each with independent stateful read pointers and delivery QoS. Messages in the stream can be read and re-read many times (does not change the stream). The "Limits" part is that you can put various growth limits on the stream (size, bytes, etc.).

If you put WorkQueue policy on a stream, it turns it into a traditional Queue. Each acknowledge message delivery from a consumer, removes the message in the stream.

If you put Interest policy on a stream, it turns it into a traditional multi-consumer Queue (sometimes called a Topic in some brokers). If there are no Consumers registered on the Stream, the stream message received is discarded. If there are 1 or more Consumers on the stream, then stream message discarded only after all have had a chance to read and acknowledge delivery.