Khalwa means seclusion but is referred to as when a man is alone with another woman, whether Muslim or non-Muslim, who is not of unmarriageable kin (mahram) within an enclosed area in such a way that a third party is unable to see or enter upon them. The prohibition of this stems from the idea of blocking the means to further harm. In other words, if we stop people from being alone, it reduces chances of the possibility of them committing Zina.

In one hadith, the Prophet ﷺ said: “No man is alone with a woman but the Shaytan is the third.” [Narrated by Ahmad, Tirmidhi and Hakim]. Shaytan whispers in to the hearts of each party and longs for them to commit Zina.

In another hadith, the Prophet ﷺ said: “Iblis [Shaytan] places his throne upon water; he then sends detachments (for creating dissension between people); the nearer to him in rank are those who are most notorious in creating dissension. One of them comes and says: ‘I did so and so.’ And he says: ‘You have done nothing.’ Then one amongst them comes and says: ‘I did not spare so and so until I sowed the seed of discord between a husband and a wife.’ Shaytan goes near him and says: ‘You have done well.’ He then embraces him.’” [Muslim]

Regardless of the wisdom, it is a clear act against the sunnah as stated in this hadith: Ibn `Abbas stated, “I heard the Prophet give a sermon. He said, ‘A man should not seclude himself with a woman except that there be with her someone who is of unmarriageable kin (mahram).'” [Bukhari, Muslim]

As stated above Khalwa is when a man and woman are alone in an enclosed room and they are not mahram. It can be difficult to apply this principle so let’s look at what does not constitute as Khalwa.

Situations not deemed to be Khalwa

1. A man and a woman stood or sat outside in public, such as a park, in a coffee shop or waiting at a bus stop.
2. A man and a woman alone in an enclosed area that other people routinely enter and exit without requiring permission, such as a shared office or a classroom or library.
3. A man and a woman alone in an enclosed area that other people do not routinely enter but is visible to others, such as a glass office.
4. A man and a woman alone in an enclosed area that other people do not routinely enter but another person is present who is either (i) a mahram or spouse, (ii) an upright non-mahram man or woman (elderly, notably righteous or a scholar), or (iii) a group of non-mahram women. So if a man and woman are in a locked room, it is not Khalwa if either of their spouses are present, or their mahrams, or if there is an upright man or woman present or a group of other women there. If there was one woman and a group of men who are not mahram then this will be considered Khalwa.
5. A man and a woman alone in an enclosed area that other people do not routinely enter but there is a barrier separating the two people for example being in the same building but two different rooms.
6. Sharing an elevator/lift
7. Sharing a car ride with a member of the opposite gender who is not a mahram with no other party inside the car and no clear barrier between the people, will not constitute Khalwa if they are driving through a built-up area. Otherwise, it would constitute seclusion, if during the night or in an isolated place.

(Ibn Abidin, Radd al-Muhtar (6:368)

Even in cases where it would not technically constitute seclusion, it may be disliked and superior to avoid unless there is some need. This due to customs of the society as well as applying the principle, “blocking the means”, which commands all Muslims to take preventative actions towards potential sins.