What's the difference between inflammation and infection? I asked it because I saw people used them interchangeably - for the same person and for the same problem?
Inflammation and infection are entirely different things, though they very often occur together.
Infection is the presence of a reproducing pathogen (bacteria, viruses etc.) in the body.
Inflammation is a common response by the body to infection or general disturbance. The details are quite complicated, but among other things, the local blood vessels open up (causing the area to swell and to get red and hot) and the immune system is activated to deal with any "invaders".
Most infections cause inflammation, but not all. Tetanus infections, for example, can happen without any inflammation, and if you have an immune deficiency (for example, due to AIDS, though that is not the only cause), inflammation can be reduced or even not happen at all.
Inflammation can also happen without infection. Things like arthritis are caused by unnecessary inflammation.