Core conceptsintermediate
Dead tuple
A row version that is no longer visible to any transaction but still occupies space on the heap page until vacuum removes it.
What this means
An old copy of a row that nobody can see anymore, left behind after an UPDATE or DELETE, but whose space isn't free yet. It stays parked on the page, taking up room, until vacuum clears it out. A pile of dead tuples is how a table quietly grows bloated.
Why it matters operationally
Dead tuples are the raw material of bloat; understanding them explains why UPDATE-heavy tables need aggressive vacuuming.
Related errors
Mentioned from
Where it lives in the source
src/backend/access/heap/pruneheap.c