I say, and with Allah's success: First: I'tikaf linguistically means to stay on something, to adhere to it, and to confine oneself to it. This is derived from His saying, Glory be to Him: {What are these statues to which you are devoted?} (Al-Anbiya: 52), and His saying, Glory be to Him: {They are devoted to idols of theirs.} (Al-A'raf: 138). Al-'akaf means confinement and stopping, as He, Glory be to Him, said: {And the sacrificial animals are to be brought to the place of sacrifice.} (Al-Fath: 25). Secondly: I'tikaf, in a technical sense, is the stay of a fasting person in a congregation mosque with the intention. He, Glory be to Him, said: {And purify My House for those who perform Tawaf and those who are in I'tikaf.} (Al-Baqarah: 125), and the linguistic meaning is present with an additional description. The congregation mosque is one that has an imam and a muezzin, and in which the five prayers are performed, or not performed. I'tikaf is not valid in a communal mosque where Friday prayers are held, even if not all prayers are performed there. Refer to: Al-Waqayah p. 244, Tabyin Al-Haqaiq 1: 347, Al-Talimat Al-Mardiyah p. 183, Al-Hadiyah Al-Alaiyah p. 183, and Allah knows best.