Short answers, pulled from the story.
The Sanskrit word avidyā appears in the Rigveda, a collection of ancient hymns dating back to the second millennium BCE. It is a compound formed by adding the prefix a- to the root vidya.
Avidyā functions as the fundamental misunderstanding regarding suffering within Buddhist doctrine. Johannes Bronkhorst states that suffering arises from actions generated by ignorance of anatta and anicca doctrines.
Avidyā is identified as the first of these twelve links in the sequence. Digha Nikaya II.55, 63 asserts that rebirth ultimately arises through a series of twelve links rooted in Avidyā.
In Suttanta literature, this ignorance refers to non-knowledge of the Four Noble Truths specifically. The Mahayana tradition considers ignorance about nature of reality and immemorial past lives to be a primordial force.
Teachings focus on a Tantric path under guidance of a teacher to remove Avidya. This method differs from other traditions by emphasizing rapid removal of ignorance through specific rituals.