safe day (in the menstrual cycle)
Refers to a day in the menstrual cycle when the risk of pregnancy from unprotected intercourse is considered low. Often used in the context of the rhythm method or fertility awareness.
Just because it's a safe day, you shouldn't neglect contraception.
排卵日 is the day of ovulation, which is typically the most fertile day, unlike a 安全日.
Compound of 安全 (safety) and 日 (day).