Awarding or being awarded the title Emperor (in German: Kaiser) was the highest political honour. It already existed during the Roman Empire, where it was originally a personal name of Julius Cesar's. (The Romans and Greeks called him "Kaisar".) Since the Roman Empire was a world power, this word was, in turn, also associated with world power. After the Roman Empire started to decline throughout Europe, the imperial rule was reintroduced by the Franconians in 800 AD. Even though there hasn't been a German emperor since 1918, the title is still in existence today. Emperors were also a part of high nobility.
The second most powerful title in the nobility order is the King (in German: König). He serves as ruler of his people and the title is usually inherited. Throughout history, secular rulers (emperors) and clerical rulers (popes) argued about who had the right to award this title. The last time Germany had a king was in 1918 and there were, in fact, five of them. Compared to other rulers, the king enjoyed additional privileges (e.g., he was addressed as "Your Majesty") and he could bestow nobility upon others.
Next in line are Dukes (in German: Herzog) and this word comes from the Latin "dux". In Germania, Dukes were originally elected military commanders. Later on in Franconia, they served as mediators between royalty and earls (sometimes referred to as counts). In fact, several earldoms were united under one duke. In Germany, there were several duchies and grand duchies until 1918, all of which were allowed to ennoble others.
Of course, the German title Prince (in German: Fürst) also belongs in this category. The word comes from the Old High German term "furisto" and was originally used to refer to the commander or leader of a political group. There is a differentiation between clerical (archbishops and bishops) and secular ones (count palatines, margraves and electors, who had the power to elect the emperor). Since 1918, no princes have had power in Germany but many exist to this day.
The next person in the line of nobility is the Earl (in German: Graf) whose role has changed significantly over time. Originally, he was equal to princes, then he lost this status and served as an official for kings and/or princes. For this position, he received some land or special privileges. Districts that were run by an earl were called earldoms (in German: Grafschaft). Later, the title Graf was still awarded but no longer came with an office.
Next in this hierarchy is the Baron (in German: Freiherr, Edelherr). The German word literally means "free man" and was used to distinguish these individuals from farmers (who were not independent). Over time, the title "baron" started to be awarded as a title of nobility (primarily in Austria but also in other parts of the world). In Prussia, it was required that future barons possessed a certain minimum amount of assets and income. In Germany, "Freiherren" are the last members of nobility to hold a title.
Knights (in German: Ritter) and Nobles (in German: Edle) are placed somewhere between nobility with a title and untitled nobility. (However in Austria, Nobles are placed into the category of untitled nobility.) While the noble status is usually inherited, this title of nobility is awarded – and sometimes only to a specific individual.
The largest group of nobility consists of untitled nobles. They are usually families of lower nobility that may or may not use one of the following nobiliary particles with their names: "v.", "v. und zu", "zu", "am" or "vom". These words are usually translated as "of" and originated in the Middle Ages when they were used to indicate from where a person comes.