On Wikipedia, Estrogens are described as a class of steroids that are important in female development and reproductive cycles. Estrone, Estriol, Estradiol are all examples of Estrogens. However, in common literature, I often see Estrogens referred to as a singular compound called Estrogen. As an example, look at the Wikipedia article for Estrogen receptor, where the authors only discuss it as a singular compound. This confuses me because if it were a singular compound, then it must have a unique chemical structure. I searched online for such a structure called "estrogen" but have only found diagrams of estrone, estriol, and estradiol. It looks like that there is no such compound called "estrogen", and that many of the books describing it are wrong on a technicality.
Could someone explain why we have this "quirk" in describing this 'nonexistent' compound called Estrogen?