N-UNCOUNT (著作、讲座、电影或绘画的)主题，题材，主要内容 The subject matter of something such as a book, lecture, film, or painting is the thing that is being written about, discussed, or shown. (著作、讲座、电影或绘画的)主题，题材，主要内容
Then, attitudes changed and artists were given greater freedom in their choice of subject matter.