"Perimenopause is the transitional period before menopause. During perimenopause, levels of estrogen, a key female hormone, start to decrease. You may begin having menopause-like symptoms, such as hot flashes or irregular periods. Perimenopause can last for years. When you go a full 12 months without a period, menopause has begun." This definition is from the Cleveland Clinic accessed on 7/10: https://my.clevelandclinic.org/health/diseases/21608-perimenopause