(To be) in heat, or she is in heat
Meanings of "(To be) in heat, or she ..."
To be in the estrous cycle. This refers to non-human mammals. This is only possible females of sexual maturity when reproductive hormones are elevated inducing the desire to reproduce, to become involved in sexual activity. This is prevalent in mammals. It can be a derogatory comment of a human female. It is most often used in referring to domestic pets, and livestock. This does not refer to the menstrual cycle. That is different. Humans have menstrual, not estrous cycles.