Pregnancy is the time during which an offspring or fetus develops in a person's uterus or womb. It occurs when an egg is fertilized by the sperm and the fertilized egg is implanted on the uterine wall. This egg then grows and forms a fetus in a span of 40 weeks (on average). These 40 weeks are referred to as being pregnant or the pregnancy period.
Sources:
https://www.britannica.com/science/pregnancy
https://www.healthline.com/health/pregnancy
https://www.betterhealth.vic.gov.au/health/healthyliving/pregnancy-week-by-week
https://www.nichd.nih.gov/health/topics/pregnancy/conditioninfo