المعنى الاصطلاحي :

To make a statement, do an act, or hold a belief that is contrary to the truth, or principally unkown.

الشرح المختصر :

"Al-jahl billah" (ignorance of Allah) is a serious malady and a fatal disease. If Allah wants goodness for someone, He teaches him what benefits him and grants him insight and thorough comprehension of His religion. "Jahl", or ignorance, is of two types: 1. Inexcusable ignorance: that stems from negligence, carelessness, or rejection despite the availability of the means of learning, whether this ignorance has to do with disbelief or sins. 2. Excusable ignorance: that stems from inability, not from carelessness or negligence; e.g. when someone grows up in the desert far away from the scholars, and it does not cross his mind that a particular deed is unlawful. If he is a Muslim, he will not be held accountable for that deed, and if he is a disbeliever, then the rulings of disbelievers is applied to him in this world, and his affair rests with Allah in the Hereafter. Some scholars say that ignorance is divided into "simple ignorance", which is being ignorant of the truth alone, and "compound ignorance", which is being ignorant of the truth in addition to believing in falsehood.