Titles
This is a list of titles for nobility and a few other groups, these are english you can go to http://www.heraldica.org/topics/odegard/titlefaq.htm for other languages or check the references list at the bottom of the page.

Title - Address - Notes
Emperor, Empress
   Your (Royal) Majesty, My Lord/Lady, Emperor/Empress Pat
   - Rules an empire.
King, Queen
   Your (Royal) Majesty, My Lord/Lady, My King/Queen, King/Queen Pat
   - Rules a country or married to the ruler. In some cases you can only inherit the title of King, if you marry the Queen you are Prince Consort.
Prince, Princess
   Your (Royal) Highness, My Lord/Lady, Prince(ss) Pat
   - Typically the son or daughter of a ruler but sometimes rule a country such as the Principality of Monaco.
Prince Consort, Princess Consort
   Your Highness, My Lord/Lady, Prince(ss) Pat
   - Married to a ruling monarch.
Regent
   Addressed as Regent or by inherited title
   - Regents rule in the stead of the crowned monarch if he/she is too young to rule or occasionally if incapable of ruling due to infirmity.
Grand Duke, Grand Duchess
   My Lord/Lady, Your Grace, Grand Duke(Duchess) Pat
   - Usually reserved for either a ruling monarch, decendants of a former ruling monarch, or rarely used instead of Prince(ss) for the offspring of a King/Queen.
Duke, Duchess
   Your Grace, Duke(Duchess) Pat
   - Nobility which holds lands within a prinicpality/kingdom, a hereditary title for the ruler of a duchy.
Margrave, Margravine
   My Lord/Lady, Lord Pat, Margrave(Margravine) Pat
   - Also called a Marquess/Marchioness. Equivalent in rank to a duke but holds land in the "marches" or border area, because conflict on borders is frequent they had broad power.
Earl, Landgrave, Count, Countess
   My Lord/Lady, Earl(Landgrave, Count etc.) Pat
   - Roughly equivalent titles, since there is no feminine term for Earl Countess is used.
Viscount, Viscountess
   My Lord/Lady, Lord(Lady) Pat, Viscount(ess) Pat
   - Title granted to someone not quite important enough to be a count but too important to be a baron.
Baron, Baroness
   -
Baronet, Baronetess
   -
Knight, Dame
   -
Reeve
   -
Squire
   -
Yeoman
   - Peasant who holds land in his/her own right.
Peasant
   - Anyone not a noble. Collectively referred to as "the commons".
Serf
   - Person bound to the land, virtually a slave to the landowner, but can free themselves by running away (usually to the city) for a year and a day.