Chickenpox is a highly contagious viral infection caused by the varicella-zoster virus. It is characterized by an itchy rash that develops into fluid-filled blisters, along with fever and fatigue. The infection is most common in children but can affect individuals of any age who have not been vaccinated or previously infected. The virus spreads through respiratory droplets or direct contact with the blisters. Vaccination is the most effective way to prevent chickenpox, and the varicella vaccine is recommended for children. Most people recover fully, but complications can occur, especially in adults and those with weakened immune systems.