What is I'tikaf?

What does I'tikaf mean?

In Terminological terms, i'tikaf means; to stay in the masjid within a certain manner with the intention of gaining the pardon of Allah by cutting all the communication and connection from the outside world in the last ten days of Ramadan.
This is a Nafila worship.
It is only wajib on condition that one takes the vow (nazr) to it.
I'tikaf an ibadah (worship) which is present both in Qur’an and in the Hadith.