Adaptive immunity is a specific immune response that develops over time after exposure to pathogens. It involves the activation of T-cells and B-cells, which recognize and remember specific antigens. Upon re-exposure to the same pathogen, the immune system mounts a more rapid and effective response due to this memorization. This immunity can be acquired through natural infection or vaccination, providing long-lasting protection against diseases. Adaptive immunity is essential for maintaining health and preventing serious infections.