The punctuation mark that shows possession or marks omitted letters in contractions such as “don’t” is the apostrophe. In a possessive expression such as “the teacher’s book,” it signals the grammatical genitive relationship; in “don’t,” it marks letters omitted from “do not.”
Apostrophes entered English writing during the 16th century, following French usage for elision. Early English writers used them when letters disappeared from a word, as in contractions. Their possessive use later became standardized, even though possession is not always literal: “today’s news” describes a relationship in time, not ownership.
A common mix-up is confusing possessive “its” with the contraction “it’s.” “Its” shows possession, as in “the dog wagged its tail,” while “it’s” means “it is” or “it has.” Apostrophes also do not normally form ordinary plurals: “apple trees” is standard, while “apple tree’s” changes the meaning to a possessive. For plural possessives, the apostrophe usually follows the plural s, as in “the players’ uniforms.”