subject matter
noun [ C ] uk/ˈsʌb.dʒekt ˌmæt.ər/ us/ˈsʌb.dʒekt ˌmæt̬.ɚ/
（谈话、写作、艺术等的）主题，题材，主要内容
the things that are being talked or written about, or used as the subject of a piece of art, etc.
The subject matter of the documentary was not really suitable for children. 这部纪录片的主题不太适合儿童。
Synonyms: message substance
See also: matter noun (SITUATION)