Setting this option allows you to specify a Form JSON file from which a set of default forms can be pre-generated when a theme containing this option is activated. This option can also be used in your theme’s functions.php file.
define( 'GF_THEME_IMPORT_FILE', 'path/to/gf_import.json' );
Note: The path is relative to your theme root.
This constant should be set in your wp-config.php. See the article Wp Config Options for more details regarding the JSON file.