The punctuation mark used to indicate possession or a contraction is the apostrophe.
In English, an apostrophe can show that one noun possesses or is associated with another: “the student’s book” means the book belonging to one student, while “the students’ books” refers to books associated with multiple students. Its placement helps distinguish singular and plural possessive forms.
Apostrophes also mark omitted letters in contractions. “Do not” becomes “don’t,” “they are” becomes “they’re,” and “it is” becomes “it’s.” This last example causes a frequent mix-up: “its” is possessive, while “it’s” means “it is” or “it has.”
The mark developed from scribal practices that used a small stroke to signal missing letters. In modern English, style guides differ on some details, especially possessives of names ending in s and the use of apostrophes for plurals. Apostrophes are generally not needed for ordinary plurals, so “apple” becomes “apples,” not “apple’s.”