Operator
Seq Scan
Sequential scan: PostgreSQL reads every row in a table from disk to find matches.
A Seq Scan reads the entire table top-to-bottom, applying any WHERE filter to each row. It is the simplest scan and is often the right choice for small tables or queries that touch a large fraction of rows.
A Seq Scan only becomes a problem when the planner uses it for a selective filter on a large table — typically because no suitable index exists, statistics are stale, or the predicate is not sargable (for example, wrapping a column in a function that the index cannot match).
If an Index Scan or Bitmap Heap Scan would be better, you usually fix it by adding an appropriate index or by rewriting the predicate so the planner can use one.