Ignorance was a quality shared by an individual or society, characterized by their possession of limited knowledge of any of a number of topics, or in general.
Roger Korby blamed ignorance and superstition for the loss of many valuable scientific discoveries. (TOS: "What Are Little Girls Made Of?")
Ignorance could be aided by the inability to read. In 2154, Sheriff MacReady preferred that the Skagaran children remain unable to read and thereby remain ignorant of the fact that Humans had initially been dominated by the Skagarans on their colony planet. (ENT: "North Star")
In 2364, when Beverly Crusher tried to protest that her son wasn't told that his actions on Rubicun III were illegal, one of the Edo mediators rebuffed her, claiming they couldn't let ignorance become a legal defense. (TNG: "Justice")
In 2365 Captain Jean-Luc Picard assured Wesley Crusher that he respected officers who admitted their ignorance rather than pridefully continuing onward and making a mess of things. (TNG: "Pen Pals")
Kolopak explained to Chakotay that he allowed him to study other cultures because he believed that ignorance was their greatest enemy. (VOY: "Tattoo")
In 2373, The Doctor was surprised to learn that Vulcans knew little about their own sexuality, saying he "fail(ed) to see the logic in perpetuating ignorance about a basic biological function". (VOY: "Blood Fever")
Ignorance was sometimes considered a preferred state of mind, as in the popular saying, "Ignorance is bliss". In 2369, Reginald Barclay mused that this was so in the case of transporters, saying they wouldn't scare him as much if he didn't know how they worked. (TNG: "Realm of Fear")
Ignorance of the final outcome of games such as baseball and, more generally, the future, only made them worth playing, according to Benjamin Sisko. (DS9: "Emissary")