media / medium
The plural, the mass noun, and agreement.
Medium is singular: Radio is a medium. Media is the plural. When media means the press as one body, it takes a singular verb: The media is covering the trial. When media means more than one medium, it takes a plural verb: Clay and bronze are both sculptural media.
Examples
Use The telegraph was the fastest news medium of the 1860s. (one channel of communication)
Use The media is camped outside the courthouse. (the press as one body)
Use The storage media are paper files and hard drives. (two separate kinds of medium)
Avoid TikTok is a media for short videos. (Change a media to a medium.)