Tdap is a vaccine that protects against three serious diseases: tetanus, diphtheria, and pertussis (whooping cough). It is recommended for preteens, teens, and adults, especially those who are in close contact with infants. The vaccine helps prevent these infections, which can lead to severe health complications. The Tdap vaccine is typically given as a single shot, and it is important to receive booster doses every ten years to maintain immunity. Pregnant women are also advised to get the vaccine during each pregnancy to help protect their newborns from pertussis.