Lafz: an uttered expression
لَفْظlafz - utterance
Learn lafz in Arabic grammar: the uttered expression that comes before asking whether speech carries recognised meaning.
Simple explanation
Scholars of Arabic begin by speaking about لَفْظ (lafz): something uttered by a human being. At this stage, we are not yet saying whether the utterance is meaningful or not.
The next question is whether that utterance has been assigned a recognised meaning in the language. This is why lafz leads naturally to مُهْمَل (muhmal) and مَوْضُوع (mawdu').