Hstore is data type for storing sets of key/value pairs in Postgres, similar to hashes in Ruby and Perl, associative arrays in PHP or dictionaries in Python.
Binary version of the json data type, used in Postgres 9.4+
I admit that gin index on hstore is much more expensive than its equivalent for jsonb but even then it is faster to just do seq scan on hstore than use index on jsonb
PostgreSQL jsonb slower than hstore for large sets of key->value
Json jsonb fields support any json-encodable data type not just key value pairs but also tend to be faster and for jsonb more compact than hstore
Django dynamic model fields