This is for those people who still do not understand why a lot of people can start removing their masks. For instance, those who have had the virus and recovered, and those who have had their vaccines. This comes from the Merriam-Webster dictionary definitions:
What is the immune system?
The immune system is what protects your body from diseases and infections. It's the bodily system that produces the immune response to defend your body from foreign substances, cells, and tissues. The immune system includes various parts of the body including the thymus, spleen, lymph nodes, special deposits of lymphoid tissue (such as those in the gastrointestinal tract and bone marrow), macrophages, lymphocytes including the B cells and T cells, and antibodies.
What is herd immunity?
The term herd immunity refers to a reduction in the likelihood of someone catching a specific infectious disease because a significant proportion of the people in that person's community are immune to it. If you are less likely to come in contact with an infectious person, you're less likely to get infected yourself. The people in a community can be immune to a particular disease especially through previous exposure or vaccination.