Mister is a title of respect used before a man's last name, like Mr. Johnson or Mr. Rodriguez. It's similar in use to titles like Miss or Mrs. for women. When you address your teacher as Mr. Chen, you're showing courtesy and acknowledging his role as an adult and authority figure.

Today it's simply a polite way to address men in formal situations. You use mister when writing someone's name in a letter, introducing someone at an event, or showing respect in professional settings. At school, you probably call your male teachers “Mr.” followed by their last names, while you might call your friends' dads “Mr. Smith” or “Mr. Patel” unless they've invited you to use their first names.

In casual speech, people sometimes use mister by itself to get someone's attention, as in “Excuse me, mister, you dropped your wallet.” The abbreviation Mr. is far more common than spelling out the full word.