What is a Kafka partition, and why does it matter for both ordering and scaling?

A topic is split into partitions, each an independently ordered, append-only log. Kafka only guarantees message order WITHIN a single partition, not across the whole topic, and partitions are the unit of parallelism — more partitions mean more consumers in a group can read concurrently, which is why partition count is a key scaling and ordering-tradeoff decision made up front.