'However, if someone makes a vow to do i'tikaf for you for one day or more,

they must fulfil their vow

[اعتكاف]

It is best done in the last ten days of Ramadan since the Prophet did that.

Linguistically it means means devotion to a thing and sticking to it.

In the Shari'a, it means that the Muslim clings to the mosque for dhikr, the prayer, recitation of the Qur'an while fasting and refraining from intercourse and things which lead to it for a day or more with an intention.

This definition includes its pillars which are: Islam, discrimination and being in a mosque, and what was mentioned of dhikr, prayer, etc, and refraining from intercourse and things leading up to it. Its pillars designate that on which the reality of the thing is based. It is an act of devotion with those qualifications.