What is the difference between a لفظ (word/utterance) and a مصطلح (term/concept), and is it permissible to coin new terms in the jurisprudential lexicon out of necessity, in light of the questions surrounding the use of the term "اختلاط" (mixing/intermingling) between genders?

The word "ikhtilat" (mixing) is mentioned in the Quran and Sunnah, and was used by Arabs to denote the mixing of two different things, as in "ikhtalat al-habl bil-nabl" (the rope got mixed with the arrows) to indicate chaos. As for the mixing of people, it is mentioned in the Prophetic Hadith: "The believer who mixes with people and endures their harm has a greater reward." And in the Hadith of Abu Usayd al-Ansari, the Prophet (peace be upon him) forbade the mixing of men and women in the street, which indicates that the prohibition of mixing between men and women is not an act of extremists, but rather a divine legislation. If it is prohibited in the street, then its prohibition in gatherings, workplaces, educational institutions, and transportation is even more paramount. The jurists of the four madhhabs and other scholars have unanimously agreed on the prohibition of the mixing of men and women, considering it an abomination, a breeding ground for fitna (temptation/strife), a cause of corruption, and a reason for the descent of punishments.