Nifaq (Hypocrisy): in the Arabic language means the general category of deception, scheming and presenting an outward appearance of good while concealing its opposite.
Hypocrisy is a serious sickness and a great crime. It means making an outward display of Islam whilst inwardly concealing kufr. Hypocrisy is more dangerous than kufr (disbelief) and the punishment for it is more severe, because it is kufr mixed with Islam and its harmful effects are greater. Hence Allaah will put the hypocrites in the lowest level of Hell, as He says:
“Verily, the hypocrites will be in the lowest depth (grade) of the Fire; no helper will you find for them.” (The Noble Quran 4:145)