Final answer:
Herd immunity is the type of immunity where a population can resist an epidemic because a high enough proportion of individuals are immune, thus providing indirect protection to non-immune individuals.
Step-by-step explanation:
The type of immunity that refers to the ability of a population to resist an epidemic is herd immunity. Herd immunity protects the entire population, including those who cannot mount an effective immune response or have not developed immunity themselves, by reducing the chance of a pathogen spreading. It occurs because the majority of the population is immune, which prevents the disease from spreading effectively amongst susceptible individuals.
Herd immunity does not depend on individual immunity, but rather on the collective immunity level within a population, which can be achieved through vaccination or natural infection. When a critical mass of the population is immune, either through vaccination or previous infection, they act as a barrier to the spread of the disease. This form of immunity is particularly crucial for protecting individuals who are not vaccinated or are unable to develop immunity, such as those with compromised immune systems.