readership; target audience
Refers to the demographic or group of people who read a particular publication, such as a magazine or newspaper.
The readership of this magazine is mainly women in their twenties.
The newspaper's readership is aging.
視聴者層 is the equivalent term for viewers (TV, video), whereas 読者層 is for readers.
Compound of 読者 (reader) and 層 (stratum, layer), literally 'reader stratum'.