What is meant by temporary zihar?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Lexically, zihar (ظِهَار) is a derivative (masdar) that originates from the verb ‘za ha ra’ (ظَاهَرَ) in the phrase ‘zahara min imra’atihi’ (ظَاهَرَ مِن َامْرَأتِهِ) which means ‘zihar of one’s wife’. In real life application, zihar refers to the words a husband said to his wife: “Anti kazahri ummi” (أنْتِ كَظَهْرِ أمِّي) which means: “You’re like my mother’s back.”
According to the 4th Edition of Kamus Dewan, zihar is an act of a husband who said words that liken one of his wife’s body parts with his mother or mahram that results in a prohibition for him from having intercourse with his wife in this situation, (the husband has to pay the kifarat (fine) for zihar). 
It is named zihar for it refers to the act that originates from the husband’s words of stating similarities of his wife with his mother’s back. The aspect of likening his wife is as though his wife is prohibited for him to have intercourse with just as it is prohibited for him to have intercourse with his biological mother or other mahrams.
The terminology zihar is defined as the words a husband uttered likening his wife who he hasn’t divorced through bain with other women who is his muabbad mahram (forever mahram). 
Allah SWT states:
الَّذِينَ يُظَاهِرُونَ مِنْكُمْ مِنْ نِسَائِهِمْ مَا هُنَّ أُمَّهَاتِهِمْ ۖ إِنْ أُمَّهَاتُهُمْ إِلَّا اللَّائِي وَلَدْنَهُمْ ۚ وَإِنَّهُمْ لَيَقُولُونَ مُنْكَرًا مِنَ الْقَوْلِ وَزُورًا ۚ وَإِنَّ اللَّهَ لَعَفُوٌّ غَفُورٌ
“Those who pronounce thihar among you [to separate] from their wives – they are not [consequently] their mothers. Their mothers are none but those who gave birth to them. And indeed, they are saying an objectionable statement and a falsehood. But indeed, Allah is Pardoning and Forgiving.” 
Imam Ibn Kathir stated in his commentary : ZIhar originates from the word al-zahr (back). The reason is the jahiliyyah people used to zihar their wives saying: “You for me is like my mother’s back.”
Whilst, according to syarak, zihar occurs for every part of the body that is analogically deduced from the back. Previously, zihar is considered as a divorce during the times of jahiliyyah. Subsequently, Allah SWT grant facilitation (rukhsah) for this ummah and set kaffarah for zihar and does not consider it as divorce as previously practised in the times of jahiliyyah.
Referring to the above verse, zihar is described as a lie or false speech. Second, it is a form of prohibition which makes it so that zihar in its true meaning is prohibited. Whereas in the book Al-Majmu’ Syarah al-Muhazzab, it is stated that it is included as a major sin and whoever commits it is considered sinful according to ijma’. 
In the following, we share several definitions presented by the mufassir regarding this verse. Among them are:
Imam al-Thabari said: And they prohibited their wives on themselves with something that Allah SWT prohibits on them which are the backs of their mothers. It is when they say to their wives: “You are like my mother’s back for me.” This is a form of divorce for a man to his wife during the times of jahiliyyah. Form Abu Qilabah, he said: “Zihar is considered as divorce during the times of jahiliyyah.” 
While Imam al-Qurthubi interprets this verse saying: The truth of zihar is likening the back of a person with another’s back. Which is likening the back that is permissible with the back of a prohibited person. Thus, the scholars have agreed (ijma’) that whoever said to his wife: “You for me is like the back of my mother,” means he has committed zihar. While most scholars are of the opinion that zihar occurs when a husband said to his wife: “You for me is like the back of my daughter or the back of my sister,” and others who are his mahram. 
According to the above question, the ruling for temporary zihar is valid for a certain amount of time.
Imam al-Nawawi said this matter is considered as conditional zihar. An example for it is: “You for me is like the backside of my mother for a month.” With this phrase, zihar applies on the wife for a month, then the duration for zihar ends and the wife returns to be permissible for intercourse just like before zihar happened. However, the husband is still sinful for the act of zihar is prohibited, even if it is just for a short amount of time. If temporary zihar is for more than four months, then it is considered like the ila’ ruling. However, the husband is not fined with kifarat ila’, if he has intercourse with his wife because of the absence of a vow. Furthermore, only kifarat zihar is applicable. 
To conclude, although the ruling of temporary zihar is valid and there is no kaffarah, however, it is still prohibited, sinful and should be avoided. In our opinion, a husband should be careful and protect his tongue from easily saying something that could harm or damage the husband and wife relationship in his marriage. May Allah SWT give us an understanding in this religion. Amin.