die Ignoranz
ignoring
The deliberate disregarding or overlooking of a person, a fact, or an opinion.
Sie bestrafte ihn für seine Bemerkung mit tagelanger Ignoranz.
She punished him for his remark with days of ignoring him.

ignorance
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ignoring
The deliberate disregarding or overlooking of a person, a fact, or an opinion.
Sie bestrafte ihn für seine Bemerkung mit tagelanger Ignoranz.
She punished him for his remark with days of ignoring him.

'Ignoranz' can mean 'ignorance' in the sense of lack of knowledge, like the English word. Much more often in German, however, it means the active, deliberate ignoring of a person. This second meaning is a common trap for learners.
Seine Ignoranz gegenüber meinen Nachrichten hat mich sehr verletzt.
His ignoring of my messages hurt me a lot.
'Ignoranz' is the noun related to the verb 'ignorieren' (to ignore). If you know the verb, you can easily work out the meaning of the noun.
Er ignoriert meine Anrufe seit Tagen.
He has been ignoring my calls for days.
When it is about deliberate disregard, 'Ignoranz' is often used with verbs such as 'zeigen' (to show), 'vorwerfen' (to accuse someone of), or the expression 'jemanden mit Ignoranz strafen' (to punish someone by ignoring them).
Sie bestrafte ihn mit völliger Ignoranz.
She punished him by completely ignoring him.
When 'Ignoranz' means ignorance or lack of knowledge, a preposition is often used to specify what the ignorance refers to. Typical constructions are 'Ignoranz in Bezug auf...' (+ accusative) or 'Ignoranz gegenüber...' (+ dative).
Seine Ignoranz gegenüber den Fakten war schockierend.
His ignorance of the facts was shocking.
stupidity
'Dummheit' and 'Ignoranz' are both negative words, but they judge different things. 'Dummheit' means a lack of intelligence or judgment, or a thoughtless action. 'Ignoranz' means either a lack of knowledge about something or the deliberate disregarding of facts, opinions, or people. The words can be confused because someone can act stupidly because of ignorance. Still, the focus is different: 'Dummheit' is about poor judgment, while 'Ignoranz' is about not knowing or disregarding something.

Die Ignoranz der Chefin gegenüber den Beschwerden des Teams macht viele wütend.
The boss's disregard for the team's complaints makes many people angry.
Aus Dummheit hat Paul seine PIN auf die Bankkarte geschrieben.
Out of stupidity, Paul wrote his PIN on his bank card.