Also called: xlog tuple/" title="Tuple">record, redo record, XLogRecord
In plain English
A WAL record is one entry in the write-ahead log describing a single change PostgreSQL is about to make. It starts with a fixed XLogRecord header (total length, transaction id, a link to the previous record’s LSN, a resource-manager id, and a CRC checksum), followed by which pages it touches and the change payload itself.
Why it matters
WAL records are the unit of durability and replication: they are written before the data pages they describe, replayed to recover after a crash, and streamed to replicas. The CRC catches corruption on replay, and the previous-LSN link chains the whole log into a verifiable sequence.