Final answer:
The pinkish-brown discharge lasting 4-10 days postpartum is called lochia serosa, which is part of the body's postpartum recovery process.
Step-by-step explanation:
The postpartum vaginal discharge that is pinkish-brown and lasts 4-10 days postpartum is known as lochia serosa. This stage follows the initial few days of thick, dark lochia rubra and precedes the final stage of lochia alba, which is a scant, creamy, or watery discharge that may continue for another 1-2 weeks. Lochia serosa is part of the body's natural process of recovery after childbirth, during which the uterine lining sheds and the site of placental attachment heals.