Index: src/wp-includes/rest-api/endpoints/class-wp-rest-terms-controller.php
===================================================================
--- src/wp-includes/rest-api/endpoints/class-wp-rest-terms-controller.php	(revision 40147)
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-terms-controller.php	(working copy)
@@ -978,7 +978,10 @@
 
 		$query_params['slug'] = array(
 			'description'       => __( 'Limit result set to terms with a specific slug.' ),
-			'type'              => 'string',
+			'type'              => 'array',
+			'items'				=> array(
+				'type'			=> 'string'
+			),
 		);
 
 		/**