Various titles are used for people in the Wizarding World. Most of them are fairly common, but a few are unique.

• Head Boy/Girl
• Headmaster/Headmistress
• Keeper of the Keys and Grounds
• Madam (Madame)
• Minister
• Mr / Mrs
• personal assistant
• Potions Master
• Prefects
• Professor
• Sorcerer
• Supreme Mugwump
• Warlock
• Witch/Wizard

Head Boy/Head Girl
There is one Head Boy and one Head Girl each year at Hogwarts. These are students in their seventh year who are given some of the responsibility of maintaining order and administering discipline. They are also in charge of the Prefects. Percy Weasley was Head Boy in his seventh year. James and Lily were also Head Boy and Girl.

Headmaster/Headmistress
The witch or wizard who runs a wizarding school such as Hogwarts uses this title. Dumbledore is currently the Headmaster of Hogwarts; McGonagall is the Assistant Headmistress. Karkaroff is Headmaster of Durmstrang while Madame Maxime is Headmistress of Beauxbatons. Portraits of previous Headmasters and Headmistresses hang in the Headmaster's Office at Hogwarts; they are all snoozing in their frames. Amando Dippet was headmaster in the 1940s when Tom Riddle was a student at Hogwarts.

Keeper of the Keys and Grounds
Hagrid's title, along with Gamekeeper.

Madam (Madame)
Witches are given this honorific. Those on staff at Hogwarts who are referred to as "madam" are those who are not professors, such as Madam Pince, the librarian, Madam Hooch, the Quidditch teacher, and Madam Pomfrey, the nurse. Others referred to in that way are Madam Malkin, who runs a robe shop in Diagon Alley, and Madam Z. Nettles of Topsham who really likes the Kwikspell course. Madam Marsh was a little old witch who rode the Knight Bus the same night as Harry. Madam Rosmerta is the proprietor of the Three Broomsticks in Hogsmeade. Madame Maxime is the Headmistress of Beauxbatons Academy.

Minister
This title is given only to the Minister of Magic, Cornelius Fudge. He is sometimes referred to simply as Minister. This is a term used for top officials in the British government, equivelent to Secretary in the U.S. Cabinet.

Mr./Mrs.
This commonplace title is used for Mr. Ollivander, Mr. and Mrs. Weasley, Mr. Filch, and even Harry himself on occasion. In the case of Filch, it may be the male counterpart of "Madam" to refer to an unmarried staff person who is not a teacher. Note that in British English, there is no period used with the abbreviation, while in the US there is.

personal assistant
Percy Weasley was made the personal assistant of Mr. Crouch. It is unclear if this was actually Crouch's intention--he, after all, didn't even remember Percy's name, and mentioned that Percy was a bit overeager. Crouch  may have done this only under the Imperious curse.

Potions Master
Why this particular branch of magic is given a special title, that of "master," is unclear. But at Hogwarts, Snape is the Potions Master. Is Sprout, then, the Herbology Master? It would seem not.

Prefects
Students who accept some responsibility for maintaining order and discipline at Hogwarts. There are several Prefects from each house (the exact number is not given, although there are clearly more than one). They are under the jurisdiction of the Head Boy and Girl. Percy Weasley was made a Prefect in his fifth and sixth years, then made Head Boy in his seventh year. 

Professor
The teachers at Hogwarts are referred to as Professors. Karkaroff of Durmstrang is also called a Professor.

Sorcerer
Almost without exception, the title of Sorcerer implies evil and Dark Magic. Voldemort is referred to as a Sorcerer. However, Dumbledore's list of titles includes that of Chief Sorcerer, and he is clearly not an evil Dark wizard. Perhaps Dumbledore has studied the Dark Arts in order to be able to fight them, thereby earning the title. As Binns states, "Just because a wizard doesn't use Dark Magic doesn't mean he can't." In Dumbledore's case, this would suggest that he has learned about Dark Magic but that he chooses not use use it, thereby demonstrating that he is not a Sorcerer and is in fact good. It is a person's choices that determine who they are, after all.

Generally speaking, sorcery is just as terrible in the Wizarding World as it is in the Muggle World. However, the term is also used for Celestina Warbeck, who is referred to as "The Singing Sorceress." Since there is nothing to suggest that she is evil, this is probably a reference to her bewitching voice as well being as a mildly clever alliteration.

The term "Sorcerer's Stone" as used in the American version of the first book was changed from the original, which was "Philosopher's Stone." The stone is not evil, even though it was given that unfortunate name by a well-meaning Americal editor.

Supreme Mugwump
The term "Mugwump" refers to a leader, derived from an Algonquian word meaning "great chief." But over the years, a number of interesting definitions have evolved for this strange word, some more flattering than others.At one time or another the term referred to a leader who stayed aloof from controversy, a somewhat humorous name for a person in authority who thinks they are more important than they are, and even a political term during the late 1800s in the US suggesting someone who sits on the fence, with their mug on one side and their wump on the other side. How this applies to Dumbledore is unclear, although he is clearly a leader in the Wizarding World and this title would suggest that. It doesn't seem likely that he would proudly claim to be self-important, so it isn't likely that the term "Supreme Mugwump" is used with its later, less complimentary meaning.

Warlock
Warlocks are older male wizards. Dumbledore is a Chief Warlock, according to his list of titles, which probably identifies him as a member of the International Federation of Warlocks. The term warlock seems to indicate only age, not temperament. There are distinguished warlocks--Ernie McMillan is more than happy to proclaim himself decedent from nine generations of them, for example. But some warlocks  get a little wild sometimes, as with the groups Harry sees in the Three Broomsticks and the Leaky Cauldron. 

• Madcap Magic for Wacky Warlocks (book)
• "Dragon breeding was outlawed by the Warlocks' Convention of 1709, everyone knows that." (Ron Weasley)
• "We would also ask you to remember that any magical activity that risks notice by members of the non-magical community (Muggles) is a serious offense under section 13 of the International Confederation of Warlocks' Statute of Secrecy." (letter to Harry from the Ministry)
• "an old warlock called Perkins" (works with Arthur Weasley)
• Warlock D. J. Prod of Didsbury (fond of the Kwikspell course)
• Professor Binns, glancing up in the middle of a deadly dull lecture on the International Warlock Convention of 1289, looked amazed.
• "I might tell you that you can trace my family back through nine generations of witches and warlocks and my blood's as pure as anyone's..." (Ernie McMillan)
• "No one wants to read about some ugly old Armenian warlock, even if he did save a village from werewolves." (Gilderoy Lockhart)
• "Fudge has been criticized by some members of the International Federation of Warlocks for informing the Muggle Prime Minister of the crisis." (apparently the Confederation is also referred to as the Federation)
• Harry ate breakfast each morning in the Leaky Cauldron, where he liked watching the other guests: funny little witches from the country, up for a day's shopping; venerable-looking wizards arguing over the latest article in Transfiguration Today; wild-looking warlocks; raucous dwarfs; and once, what looked suspiciously like a hag, who ordered a plate of raw liver from behind a thick woollen balaclava. 
• A curvy sort of woman with a pretty face was serving a bunch of rowdy warlocks up at the bar.