Kafka Streams: A KStream is a record stream, a KTable is a changelog

StreamsBuilder builder = new StreamsBuilder();

KStream<String, Order> orders = builder.stream("orders");
KTable<String, Customer> customers = builder.table("customers");

orders.join(customers, (order, customer) -> enrich(order, customer))
      .to("orders-enriched");

KStream: every event, including three updates to the same key
KTable:  one row per key, updated in place