What is the definition of khalwa, and is the presence of a woman with an unfamiliar man inside a car or in a room with an open door for the purpose of teaching considered khalwa?

Unlawful seclusion (al-khalwa (definition) al-muharramah) is when a man is alone with a woman who is a stranger to him, meaning she is neither his wife nor his mahram (definition). The basis for its prohibition is the Prophet's (peace be upon him) saying: "No man should seclude himself with a woman except with a mahram." Seclusion in a car is considered part of this. As for a woman sitting with a strange man for learning in a room with an open door, it is permissible if a mature mahram can see them, and provided the woman adheres to her hijab (definition). Otherwise, it is an unlawful seclusion.