broad-mindedness; magnanimity; generosity of spirit
Describes a person's capacity to accept others' opinions, forgive mistakes, and remain calm under pressure. Often used in contexts praising someone's character.
I'm always impressed by his broad-mindedness.
What is required of a leader is magnanimity.
心が広い is a more colloquial adjective phrase meaning 'broad-minded'. 度量の広さ is a formal noun often used in evaluative or descriptive contexts.
Compound of 度量 (どりょう, 'capacity, magnanimity') and 広さ (ひろさ, 'breadth, wideness'). The word 度量 originally referred to a measuring container, later extended metaphorically to a person's mental capacity.