Understanding Heap Index in Postgresql

On Postgresql 12, given: postgres=# \d bip Table "public.bip" Column | Type | Collation | Nullable | Default --------+---------+-----------+----------+--------- a | integer | | not null | Indexes: "foo_idx_a" hash (a) I then ran a explain select ...: postgres=# explain select * from bip where a = 42; QUERY PLAN ------------------------------------------------------------------------- Bitmap Heap Scan on bip (cost=4.10..14.80 rows=13 width=4) Recheck Cond: (a = 42) -> Bitmap Index Scan on foo_idx_a (cost=0.00..4.10 rows=13 width=0) Index Cond: (a = 42) (4 rows) What is the meaning of the Recheck Cond: (a = 42) in the EXPLAIN output?