Infections are illnesses caused by germs. They can be any kind of germ (see Germs — Differences Among Them). It’s a common mistake to think that somebody with an infection needs antibiotics, because common antibiotics only kill bacteria, not other kinds of germs. Many infections get better on their own. If we give antibiotics when not necessary, not only are they useless, and raise risk for allergic reaction or side effects. But more importantly, bacteria living harmlessly within us can become resistant, in which case the antibiotic may not work in the future when it might be really necessary.
The symptoms of infection depend on the part of the body and the germ involved. Fever may be a symptom for any kind of germ, although it can also occur with illnesses that have nothing to do with germs. For bacterial infections in just one part of the body, pain is a common symptom. Symptoms of infection are almost always caused by the reaction of our immune system, and not by the germ itself.
It’s common to have germs in a part of the body without infection being present, For example, all sorts of bacteria live harmlessly in our mouth, but cause terrible illness if they get into the lung, a tooth root, or rarely the heart or brain. On the other hand, some people have the Strep Throat bacteria living harmlessly in the throat. If we get sick from a virus, and they find Strep on a throat swab, it doesn’t prove 100% that it’s the cause. Germs can infect any part of our body. The infections are usually named by the Greek word for the body part, plus “-itis” which means inflammation or infection. So infection of the liver is “hepatitis” (“hepa-” means liver in Greek); of the brain there’s meningitis and encephalitis (meningeal membranes cover the brain; “encephalo-” means the brain itself); appendicitis is infection of the appendix, etc. etc. etc.