The word jahl is often translated as ignorance. Ignorance is translated as a lack of knowledge and information. According to the school of Ahl al-Bayt (as), this translation is wrong. 

Most often than not, the word jahl in Islam means foolishness. 

For example, if you look at the first volume of Usul al-Kafi, one of Islam’s most important books of hadiths, one of the beginning chapters is called Kitab al-Aql wa al-Jahl, meaning “The Book of the Intellect and Foolishness.”  

If you go through the book, you will also notice another chapter called “the Book of the Excellence of Knowledge”. Notice here that the word Jahl is not juxtaposed with Ilm or knowledge, but it is contrasted with Intellect.  

So here it becomes pretty obvious that Jahl is foolishness, and really, this is what makes sense. Conceptually speaking, the word jahl is similar to the word safaaha in Arabic, which means idiocy and foolishness.  

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