Information and entropy. Thus information is like energy, in the sense that knowing the amount of energy does not tell you anything about its nature, location, form, etc. The same is true with information. Entropy is a particular kind of information. It is the information you do not have about a situation.
Information is subjective.
You know things that I don't. This is, after all, why communication is useful. Strictly speaking, yes. However, in physical situations the difference of entropy as perceived by two observers may be negligibly small. Information is measured in bits.