निम्नलिखित में से किस शब्द को सिविल प्रक्रिया संहिता, 1908 की परिभाषा धारा (धारा 2) में स्पष्ट रूप से परिभाषित नहीं किया गया है?

Under Section 113 of the CPC, a Reference can be made to the High Court during the pendency of a case when:

The purpose of ________ is to enable subordinate courts to obtain, in non-appealable cases, the opinion of the High Court on a question of law and thereby avoid the commission of an error which could not be remedied later.