DPT3 refers to the third dose of the Diphtheria, Pertussis (whooping cough), and Tetanus vaccine, commonly administered to children. It is part of the routine immunization schedule and is typically given at ages 6 months, 18 months, and 4-6 years. This vaccine helps protect against these three serious bacterial diseases, which can cause severe complications. DPT3 is crucial for building immunity and preventing outbreaks in the community.