وَالْبَلَاغَةُ: وَهِيَ تُنْبِئُ عَنِ الْوُصُولِ وَالِانْتِهَاءِ
Balagha originally conveys reaching and arriving at an endpoint.
Wusul indicates reaching a destination, while intihaʾ indicates arriving at the intended limit. The linguistic association helps explain the concern for expression that reaches its communicative goal.
But mere successful transmission is not the full technical definition. The demands of the situation, fasaha, and further conditions will also matter.