The concept for the new app was born during a brainstorming session.

was 是 be 动词的过去式，表示"是"或"存在"的状态。 born 是动词 bear 的过去分词形式，bear 本意是"承受、生产"，在这里表示"诞生、产生"的概念。 was born 是一个固定搭配，表示"诞生、产生"的意思，常用于描述想法或概念的起源。