A hen is a mature female chicken, as opposed to a pullet.
Hen might also refer to the female of other bird species, like hen turkey as opposed to tom turkey.
Most supermarket chickens, marked “Broiler/Fryers” are adolescents, about 8 weeks old. Roasters are a little older, but still under 8 months and weigh up to about 5 pounds. Hens are grown up girl chickens more than a year old and there’s no definitional weight or age limit. Yours may have indeed been a genuine hen, at that size. That’s why it was so tough when you roasted it. Honestly, I’m going to check out Walmart next week for actual hens…they’re really hard to find, are usually stupid expensive and have a much more chickeney flavor if you cook them right - which is in stews or stock. My Sherried Chicken is over the top with an actual hen.
If you want to roast a chicken, find one under 5 pounds.
Even in natural insemination, it only takes one rooter to inseminate dozens of hens. Before factory farming, most of the chickens people ate were roosters or male adolescents, because you just don’t need many roosters around to keep getting new eggs and chickens, and they’re annoying as hell with all that crowing (which is not only at dawn, it’s all day long.)