Immunity is the protection against pathogens or infectious diseases. Immunity develops after antibodies to the disease are produced in the body. Types of immunity include innate, adaptive, active and passive.
Active immunity refers to protection from a disease through a previous infection or through vaccinations. Passive immunity occurs when the antibodies come from elsewhere.
In Our Own Words
Immunity is protection from illness due to the action of the immune system. Your immune system fights pathogens (i.e., any organism that can enter the body and make you sick) in two basic ways. The first way is the shotgun approach, better known as innate immunity, which protects generally against many different invaders and does not require antibodies. There is also the highly specific approach of adaptive immunity, which protects against distinct viruses or bacteria.
Immunity to a specific invader is considered active immunity when the body makes antibodies in response to exposed germs or to vaccines. Its known as passive immunity when an individual does not self-produce antibodies and receives them instead. For example, babies have passive immunity when their moms antibodies cross the placenta to help out in the newborn period. Administration of certain blood products that contain antibodies can also give people passive immunity.