noun
readership; target audience
Refers to the demographic or group of people who read a particular publication, such as a magazine or newspaper.
この雑誌の読者層は主に20代の女性です。
The readership of this magazine is mainly women in their twenties.
新聞の読者層が高齢化している。
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'.