forms of the media, especially traditional forms such as newspapers, television, and radio rather than the internet, that influence large numbers of people and are likely to represent generally accepted beliefs and opinions

The mainstream media seemed to completely ignore the protests. 主流媒体似乎完全无视抗议活动。

Mainstream media is always going to take a couple of years to catch onto what 20-year-olds are thinking. 关于20多岁的年轻人在想什么，主流媒体总是要滞后几年的时间。