The verb "avoir" is a fundamental French verb that means "to have." It is used to indicate possession, such as owning something or having a certain quality. For example, in the sentence "J'ai un livre," which translates to "I have a book," "avoir" shows ownership of the livre. In addition to possession, "avoir" is also used in various expressions and as an auxiliary verb in compound tenses. For instance, in the phrase "J'ai mangé," meaning "I have eaten," "avoir" helps form the past tense. Understanding "avoir" is essential for mastering the French language.