Also called: enable_seqscan, enable_indexscan, enable_hashjoin
In plain English
The enable_* settings (enable_seqscan, enable_indexscan, enable_hashjoin, and friends) let you discourage a particular strategy. Turning one off does not truly forbid it — it adds a large penalty to that path’s cost so the planner picks something else if it can.
Why it matters
They are diagnostic tools: flip one off, re-run EXPLAIN, and see what the planner would otherwise have chosen and at what cost. That tells you why a strategy won. They are not meant for production — the right fix is usually better statistics or tuned cost constants, not a permanently disabled scan type.