Event

An event is the fundamental unit of data in Kafka: an immutable record, published to a topic, representing a business fact that already occurred — "payment approved," "PIX received," "account blocked." Unlike a command (which instructs a future action), an event only reports something that already happened; whoever consumes it independently decides what to do with that information. It's this nature — a past fact, not an instruction — that lets multiple consumers react to the same event in completely different ways, without the producer needing to know any of them.