Honorific

An honorific is a title that shows esteem, courtesy, or respect for position or rank. It is used when addressing or referring to a person. Sometimes, the term "honorific" is used in a more specific sense to refer to an honorary academic title.
In the world of the past honorifics were highly visible. The difference between "Miss" and "Mrs" was fundamental in British social life (and, with variations, throughout Europe). It was not voluntary: you did not write a letter to a female without using the correct prefix.
Technical prefixes could be tricky. What do you do if the recipient has several positions or degrees? In German, you would list them all: Herr Dr. Dr. Professor Professor (then addressee's surname). In English, the postscript Esq., for "Esquire" was usually added for a man.
If the person used the prefixes to refer to himself, that was regarded as low behaviour, egotistical. The one exception was the medical doctorate in the UK. A medical doctor could described himself as Dr. Brown, and he would be understood as being a medic. There were originally no PhDs awarded in British universities, and they were uncommon until after the Second World War. Civil servants signed letters "Your obedient servant" to emphasize their intermediate role between government and the people, or between Parliament and the people.
It is obvious that the Church and the Armed Forces have honorifics of their own. If, as in the Armed Forces, the use of honorifics is compulsory, are they really honorifics? Similarly with the Royal Families. Compulsory honorifics have been going out of favour. They can be enforced in some cases, but the tendency is to drop them in informal life.