What is an offset in Kafka?

An offset is a 64-bit integer that identifies a record's position within one partition; the log doc calls it the message ID in that partition. Offsets are assigned per partition, so the same offset number appears in every partition of a topic, and a record is located by topic, partition and offset. A new partition starts at offset 0 and offsets grow as records are appended. An offset never changes once assigned, even when compaction removes earlier records, so gaps can appear. A consumer's position in each partition is a single integer: the offset of the next record it will consume. Committing an offset saves that position; the committed offset is the next record to process (last processed offset plus one), not the last one processed.

Expected key concepts: offset, 64-bit integer, position, per partition, never changes, position, next record, commit, last processed offset plus one